Advertisement

International Journal of Metalcasting

, Volume 13, Issue 2, pp 426–437 | Cite as

Effects of Al–Ti–C–Ce Master Alloy on Microstructure and Mechanical Properties of Hypoeutectic Al–7%Si Alloy

  • Wanwu DingEmail author
  • Xiaoyan Zhao
  • Wenjun Zhao
  • Tingbiao Guo
  • Xinchang Tang
  • Jisen Qiao
  • Tiandong Xia
Article
  • 117 Downloads

Abstract

It is well known that the mechanical properties of hypoeutectic Al–7%Si alloys are influenced by the size, morphology, and distribution of primary α-Al and eutectic Si crystals. In the present work, a novel Al–TiCCe master alloy was prepared by the pure molten aluminum thermal explosion reaction, and its effects on the microstructure and mechanical properties of hypoeutectic Al–7%Si alloy were investigated. The results show that the Al–TiCCe master alloy containing α-Al, granular TiC, lump-like TiAl3, and block-like Ti2Al20Ce has excellent refining and modification properties for hypoeutectic Al–7%Si alloy. When 1.5 wt.% Al–TiCCe master alloy is added, the coarse dendritic α-Al in hypoeutectic Al–7%Si alloy is refined into equiaxed grains. The secondary dendritic arm spacing (SDAS) was also reduced, and the coarse needle-flake eutectic Si phase was transformed into a fibrous and granular phase. It was found that the ultimate tensile strength and elongation increased by 59% and 56%, respectively, due to the decrease in the SDAS of primary α-Al dendrites and the modification of eutectic Si crystals. Moreover, the change of mechanical properties corresponds to the evolution of microstructure.

Keywords

hypoeutectic Al–7%Si alloy Al–TiCCe master alloy microstructure mechanical properties 

Introduction

Hypoeutectic Al–7%Si alloys are widely used in aerospace, automobile, and motorcycle manufacturing, as well as other fields, because of their high strength, low density, and excellent casting properties.1, 2, 3, 4, 5, 6 However, the α-Al phase comprises of coarse dendrites in hypoeutectic Al–7%Si alloy without refinement and modification, while the eutectic Si phase is coarse needlelike or platelike, which seriously reduces the mechanical properties of the alloy.7,8 Therefore, it is important to research the grain refinement of α-Al phase and the modification of eutectic Si phase in hypoeutectic Al–7%Si alloy for enhancing the mechanical properties of hypoeutectic Al–7%Si alloy.9

At present, the main modification elements are Na, Sr, Sb, etc., which can effectively improve the morphology of Si phase in Al–7%Si alloy and improve the mechanical properties of Al–7%Si alloy.10, 11, 12 However, there are some problems in the use of these modifiers, such as high cost and short duration of refinement and modification. In recent years, the unique chemical activity and surface adsorbability of single rare-earth (RE) elements or mixed RE elements have been recognized by many researchers,13, 14, 15, 16 who have tried to use them in the modification process of Al–7%Si alloys. Some studies have shown that14, 15, 16, 17, 18 La, Y, Ce, Er, and other RE elements have good modification and long-term effect. Based on the present state of research, RE elements have a certain modification effect on the eutectic Si phase, but which RE elements are more suitable as a modifier, the mechanism of modification, and the properties of the modified alloys still need to be further studied.

It is well known that Al–Ti–B and Al–Ti–C master alloys are considered to be good refiners for aluminum and its alloys.19,20 Compared with TiB2 in Al–Ti–B master alloy, TiC particles in Al–Ti–C grain refiner have less tendency to be used as heterogeneous nucleating core and are not affected by elements such as Zr, Cr, Mn, and V. Therefore, the preparation, microstructure, and properties of Al–Ti–C master alloy have received more attention.19, 20, 21 It has been found that A1–Ti–C alloy has good refining effect on α-Al phase grains in hypoeutectic Al–7%Si alloy, but the modification effect on the eutectic Si phase is not satisfactory.22,23 Therefore, it is necessary to develop a master alloy that can refine α-Al phase grains and modify the eutectic Si phase at the same time. Although some scholars have successfully prepared Al–Ti–B–Sr,24 Al–Ti–C–Sr,25 and Al–Ti–C–RE26,27 alloys with grain refinement and modification effects using the fluorine salt and doping methods, due to the mutual poisoning of B and Sr28,29 or to the complex preparation process, there has been no industrial application.

RE oxides have been widely used as reaction promoters in the preparation of composite materials,30,31 but their application in the synthesis of Al–Ti–C master alloys has not been frequently reported. Wang et al.32 studied the effect of CeO2 on the thermodynamics of Al–Ti–C–RE prepared by the fluorine salt method, and the results show that the addition of CeO2 reduces the reaction temperature of the prepared alloy. The author also found that the addition of CeO2 can improve the wettability of C and Al melts and promote the formation of TiC particles.33 But there are many problems; for example, the refining and modification efficiency of master alloy on industrial pure aluminum and hypoeutectic Al–8%Si alloy are not very satisfactory. For this reason, the author has carried out a lot of research work and further optimized the process parameters of the alloy. In this paper, a new type of Al–TiCCe alloy was prepared by the authors and its effect on the microstructure and mechanical properties of hypoeutectic Al–7%Si alloy were reported.

Experimental Procedures

The main raw materials for the preparation of Al–TiCCe master alloy include Al powder (99.6%, 61–74 μm in size), Ti powder (99.3%, 38–44 μm in size), C powder (99.8%, 11–30 μm in size), CeO2 powder (99.5%, 1–2 μm in size), and commercial pure Al (99.7%). First, the Al, Ti, C, and CeO2 powders are converted into precast blocks (Φ 25 mm × 50 mm) by ball mixing and cold pressing under a pressure of 50–60 MPa. The molar ratio of Al, Ti, and C powder is 5:2:1 in the prefabricated blocks, while the content of CeO2 is 4 wt.%. Second, the prefabricated block is added to a 820 °C aluminum melt. Approximately 10–15 min later, a graphite rod is used to stir the aluminum melt, and then the melt was held for 5 min at 820 °C. Finally, the melt was poured into a preheated (200 °C) cylindrical steel mold (50 mm in inner diameter and 30 mm in height) on a fire brick.

The Al–7%Si alloy was prepared using commercial Al–12%Si master alloy and commercial pure Al (99.7%) in a clay-bonded graphite crucible by a 7.5 kW well-resistance furnace. The chemical composition of Al–7%Si alloy is presented in Table 1. The Al–7%Si alloy was remelted at 730 °C and held for 5 min in a clay-bonded graphite crucible by an electrical resistance furnace. And then a certain amount (0.5, 1.0, 1.5, and 2.0 wt.%) of Al–TiCCe master alloy was added into the melt at 730 °C. The melt was stirred thoroughly to ensure the homogeneity of the composition, and then the melt was held for 10 min at 730 °C. After the melt was degassed using commercial degasser of solid hexachloroethane (C2Cl6) and the slag was skimmed, the melt is divided into two parts, one of which is cast in a steel mold (50 mm in inner diameter and 30 mm in height) to obtain macrorefined samples. The other part was directly poured into a preheated (200 °C) book steel mold (20 mm in inner diameter and 120 mm in length) at 730 °C to obtain the tensile test bars.
Table 1

Chemical Compositions of the Base Al–7%Si Alloy

Alloy

Elements (wt.%)

Si

Mg

Fe

Cu

Mn

Ti

Zn

Al

Al–7%Si

7.01

0.02

0.23

0.02

0.01

0.02

0.02

Bal

The phase composition of Al–TiCCe master alloy was identified using a Rigaku D/max-A X-ray diffractometer (XRD, PW 3040/60, PANalytical, Rotterdam, The Netherlands) with a range of 0.02° for each step, 2θ, and 20°–90° for Cu K radiation, and an image plate detector. The composition of the master alloy was measured using inductively coupled plasma atomic-emission spectrometry (ICP-AES, HK-8100, Beijing Huake Yi Tong Analytical Instrument Co. Ltd.) and an infrared carbon apparatus (CS-320C, Chongqing Research Rui Instrument Co. Ltd.). The chemical composition of Al–TiCCe master alloy is presented in Table 2. The microstructure of the samples was characterized by large optical microscope (OM, MEF3, Leica, Inc., Vienna, Austria) and a JSM-7500 scanning electron microscope (SEM, SSX-550 fitted with EDS equipment, Shimadzu Corp., Kyoto, Japan) after rough grinding, finishing of the grinding, and electrolytic polishing (10% HClO3 + 90% absolute alcohol, electrolyte composition in volume fraction, 20 V voltage). The average macroscopic grain size was determined by the linear intercept method. The secondary dendrite arm spacing (SDAS) and silicon particle size were measured and counted by Nano Measurer 1.2 image analysis software.
Table 2

Chemical Compositions of the Al–TiCCe Master Alloy

Alloy

Elements (wt.%)

Ti

C

Ce

Fe

Cu

Ti

Zn

Al

Al–TiCCe

4.91

0.62

0.35

0.25

0.04

0.03

0.04

Bal

According to GB/T 228-2002, the tensile test bars were processed from the cast round bars and then to evaluate the mechanical properties of the samples with different contents of Al–TiCCe master alloy. Figure 1 shows the configurations of the samples used for tensile tests. Tensile tests were carried out under the condition of room temperature and strain rate of 0.5 mm/min by using an MTS810 machine (MTS System Company, Eden Prairie, MN, USA). The tensile strength and elongation data of each alloy reported below are average values of three tensile specimens. The fracture surfaces of tensile specimen were analyzed by SEM to evaluate the fracture mechanism.
Figure 1

Dimensioned schematic of the tensile specimen (unit: mm).

Results and Discussion

Microstructure of Al–TiCCe Master Alloy

Figure 2 shows the XRD pattern of the prepared Al–TiCCe master alloy. It can be seen that, compared with Al–Ti–C,34 the Al–TiCCe master alloy not only contains α-Al, TiAl3, and TiC, but also contains Ti2Al20Ce phase. Figure 3 shows the microstructures of Al–TiCCe master alloy. From Figure 3a, it can be seen that a large number of block-like particles are distributed on the aluminum matrix, most of which are gray, with some of them being bright white. In addition, it can be seen from Figure 3b that most of the granular particles are agglomerated at grain boundaries. To identify the different phases, EDS analyses were performed on the different particles. Based on the energy spectrum analysis of Figure 4a–c and analysis of the XRD pattern, the bright-white block-like particles were determined to be Ti2A120Ce, the gray lump-like particles TiAl3, and the granular particles TiC.
Figure 2

XRD pattern of Al–TiCCe master alloy.

Figure 3

Microstructures of Al–TiCCe master alloy: (a) SEM image and (b) SEM image of TiC.

Figure 4

EDS composition analysis of points A, B, and C in Figure 2: (a) point A; (b) point B; and (c) point C.

Compared with the Al–Ti–C master alloy,34 a new phase, Ti2Al20Ce, has appeared in Al–TiCCe master alloy. The reaction mechanism might have occurred as follows. In the reaction process, the addition of CeO2 improved the wettability of Al powder, Ti powder, C powder, and aluminum melt, and the aluminum thermal reaction formed TiAl3 phase and part of the free state [Ti]. Under the energy supplied by the aluminum thermal reaction, CeO2 can participate in the carbon thermal reaction with C, and the continuous heat of the reaction will be conducive to the formation of TiC particles and will generate active [Ce]. The main reaction equations are
$$ {\text{Ti}} + 3{\text{Al}} = {\text{TiAl}}_{3} , $$
(1)
$$ {\text{CeO}}_{ 2} ({\text{s}}) + 4{\text{C}}({\text{s}}) = {\text{CeC}}_{2} ({\text{s}}) + 2{\text{CO}}({\text{g}}) \uparrow , $$
(2)
$$ {\text{CeC}}_{ 2} ({\text{s}}) + 2{\text{Ti}}({\text{s}}) = 2{\text{TiC}} + [{\text{Ce}}], $$
(3)
$$ {\text{C}}({\text{s}}) + {\text{Ti}}({\text{s}}) = {\text{TiC}}. $$
(4)

Finally, the reaction of TiAl3 and [Ce] creates a new Ti2Al20Ce phase in the solidification of molten alloy, while CeO2 is the promoter of reactants and reactions. However, these theories are preliminary speculation and are consistent with those advanced by Wang et al.32 Further in-depth study and analysis on the thermodynamics and dynamics are needed in the future.

Effect of Al–TiCCe Master Alloy on Microstructure of Hypoeutectic Al–7%Si Alloy

Figure 5 shows the macrostructures of hypoeutectic Al–7%Si alloy with different additions of Al–TiCCe master alloy. It can be seen that compared with hypoeutectic Al–7%Si alloy without adding Al–TiCCe master alloy, the macroscopic grain of hypoeutectic Al–7%Si alloy with adding 0.5 wt.% Al–TiCCe master alloy have been refined obviously, and the original coarse columnar grain has been replaced by fine equiaxed grain. As the addition of Al–TiCCe master alloy increases, the macroscopic grains of hypoeutectic Al–7%Si alloy become more refined. However, when the addition amount of Al–TiCCe master alloy is increased from 1.5 to 2%, the macroscopic grains begin to coarsen. As can be seen from the average macroscopic grain size curve of hypoeutectic Al–7%Si alloy with different Al–TiCCe master alloy additions in Figure 6, as the Al–TiCCe master alloy addition increases from 0 to 1.0%, the average macrograin size of hypoeutectic Al–7%Si is refined from 1780 to 230 μm. When the addition increased from 1.5 to 2%, the average macroscopic grain size increased from 255 to 420 μm.
Figure 5

Macrostructures of Al–7%Si alloy with different additions of Al–TiCCe master alloy: (a) unrefined; (b) 0.5 wt.%; (c) 1.0 wt.%; (d) 1.5 wt.%; (e) 2.0 wt.%.

Figure 6

Average macroscopic grain size of Al–7%Si alloy with different additions of master alloy.

Figure 7 shows the microstructures of α-Al in hypoeutectic Al–7%Si alloy with different additions of Al–TiCCe master alloy. It can be seen from Figure 7a that the α-Al dendrites of hypoeutectic Al–7%Si alloy without refinement and modification are coarse dendritic. It has clear primary and secondary branches and irregular appearance. From Figure 7b–d, we can observe that there is an optimal refining effect when the addition amount of Al–TiCCe master alloy is 0.5–1.0%. The primary α-Al dendrites are obviously refined and the primary and secondary dendrites also decrease and the shape is regular. However, when the content of Al–TiCCe master alloy is 2.0%, the α-Al dendrites began to change into dendrites. This proves that, with a certain addition level, the Al–TiCCe master alloy has a good effect on the refinement of α-Al dendrites in hypoeutectic Al–7%Si alloy.
Figure 7

Microstructures of α-Al in Al–7%Si alloy with different additions of Al–TiCCe master alloy: (a) unrefined; (b) 0.5 wt.%; (c) 1.0 wt.%; (d) 1.5 wt.%; and (e) 2.0 wt.%.

To further investigate the effect of adding different amounts of Al–TiCCe master alloy to eutectic Si, the microstructure was characterized by high-magnification optical microscopy and scanning electron microscopy, as shown in Figures 8 and 9. It can be seen from Figures 8a and 9a that the eutectic Si in the hypoeutectic Al–7%Si alloy without adding any master alloy is coarse and needle-flake-like and is distributed around the α-Al dendrites. When adding 0.5 wt.% Al–TiCCe master alloy into the hypoeutectic Al–7%Si alloy, the eutectic Si changes from coarse needles to short rods, with some of them still needle-flake-like, as shown in Figures 8b and 9b, indicating that the eutectic Si in hypoeutectic Al–7%Si alloy is not sufficiently modified by adding 0.5 wt.% Al–TiCCe master alloy. When the addition of Al–TiCCe master alloy was increased from 1.0 to 1.5 wt.%, the eutectic Si became fibrous and characterized by small granules. However, some fibrous eutectic Si began to coarsen into coarse needle shapes and large granular shapes when the addition continued to increase to 2 wt.%. It can be seen that the addition of 1.5 wt.% Al–TiCCe master alloy has a good modification effect on the eutectic Si in hypoeutectic Al–7%Si Alloy.
Figure 8

Microstructures of eutectic Si in Al–7%Si alloy with different additions of Al–TiCCe master alloy: (a) unmodified; (b) 0.5 wt.%; (c) 1.0 wt.%; (d) 1.5 wt.%; and (e) 2.0 wt.%.

Figure 9

Magnified images showing effects of Al–TiCCe master alloy on eutectic Si structure in Al–7%Si alloy: (a) unmodified; (b) 0.5 wt.%; (c) 1.0 wt.%; (d) 1.5 wt.%; and (e) 2.0 wt.%.

Figure 10 shows the relationship between the addition of Al–TiCCe master alloy and the secondary dendritic arm spacing and size of eutectic Si in hypoeutectic Al–7%Si alloy. It can be seen that the secondary dendritic arm spacing and the eutectic Si size in hypoeutectic Al–7%Si alloys first decreased and then increased with increasing Al–5Ti–0.62C–0.2Ce master alloy content. The addition of 1.0–1.5 wt.% Al–TiCCe master alloy can not only refine α-Al dendrites, but can also have a better modification effect on the eutectic Si in hypoeutectic Al–7%Si alloy.
Figure 10

Relationship curve between the addition level of Al–TiCCe master alloy and the SDAS and eutectic Si size in Al–7%Si alloy.

It is well known that when the master alloy is added to the aluminum melt, the aluminum base of the master alloy will melt rapidly and release a large number of α-Al heterogeneous nucleation particles35,36 or Si-modified elements. In the present work, compared with Al–Ti–C, the Al–TiCCe master alloy not only contains more TiC and TiAl3 particles, but also contains Ti2A120Ce. When Al–TiCCe master alloy is added to the aluminum melt, the TiC released from the Al–TiCCe master alloy matrix can be used as a good nucleating agent for α-Al because of the low lattice mismatch between TiC and α-Al37,38 and the activity and stability of TiC with the assistance of TiAl3 (i.e., the formation of a Ti–rich layer39,40) during the refining process. While the Ti2A120Ce will dissolve and provide a large amount of free Ce atoms for the aluminum melt, it has been reported that Ce and other RE elements have good modification and long-term effects.14,17 Therefore, with increasing Al–TiCCe master alloy content and the dissolution of Ti2A120Ce, there is a large amount of free active Ce in the aluminum melt. From the perspective of twin geometric growth,41 because the atomic radius of Ce is 0.183 nm and that of Si is 0.143 nm, and the ratio of the two is 1.280, which is very close to 1.648, Ce plays a leading role in the modification of the Si phase.

It has been reported that, in the case of grain refinement of Al–Si alloys, Ti in the master alloy and Si can be coated with Ti silicide on the surface of TiAl3, which poisons the effectiveness of the nucleation in the master alloy.42 Qiu et al.43 also found that the crystal matching of Ti5Si3 and TiAl3 is better than that of Al matrix. Therefore, the Ti content in the master alloy should be kept at a low level when the Al–Si alloy is refined.44 In our experiment, an increase in SDAS and eutectic Si coarsening appeared when the addition amount of Al–TiCCe master alloy reached 2 wt.%. This phenomenon is consistent with the above research reports. The main reason may be that when the addition of Al–TiCCe master alloy exceeds 1.5 wt.%, with the increase in master alloy addition, there will be excess Ti in the melt, which will form titanium silicide with Si. It not only poisoned the nucleation efficiency of TiAl3 and TiC, but also affected the modification of Ce. However, the theoretical analysis is an inferential model up to now because no direct experimental proof has been observed, so further study will be made in the future.

Effects of Al–TiCCe Master Alloy on Mechanical Properties of Hypoeutectic Al–7%Si alloy

Figure 11 shows the trend of tensile strength and elongation of Al–7%Si alloy with the addition of Al–TiCCe master alloy. It can be seen that Al–TiCCe master alloy has a significant effect on the tensile properties of Al-7%Si alloy. The tensile strength and elongation of Al–7%Si alloy without the addition of master alloy are 156 MPa and 4.3%, respectively. With increasing Al–TiCCe master alloy content, the tensile strength and elongation first increased and then decreased. When the amount of Al–TiCCe master alloy added was 1.5%, the tensile strength and elongation reached their peaks, 248 MPa and 6.7%, an increase of 59% and 56%, respectively. However, the tensile strength and elongation of Al–7%Si alloy decreased obviously upon further increasing the amount of Al–TiCCe master alloy added. Al–TiCCe master alloy refines α-Al dendrites and modifies Si particles, which is the important reason for the change in the properties of hypoeutectic Al–7%Si alloy. Decreasing Si particle size and increasing roundness decrease the probability of Si particle cracking and increase the resistance of microcrack initiation. In addition, the refinement of α-Al grains leads to the increase in resistance of dislocation movement. As a result, the work-hardening rate of the α-Al matrix increases, and the deformation of the alloy can be carried out in a more coordinated manner, thus effectively preventing the accumulation and growth of microcracks. Therefore, under tensile load, the alloy can withstand more deformation, and the strength and plasticity of the alloy can be improved obviously.
Figure 11

Mechanical properties of Al–7%Si alloy with various concentrations of Al–TiCCe master alloy.

Figure 12 shows the fracture morphology of hypoeutectic Al–7%Si alloy for different Al–TiCCe master alloy contents. As shown in Figure 12a, a clear cleavage surface can be seen in the fracture structure of the unrefined Al–7%Si alloy, which shows the typical brittle fracture nature. This is because the Al–7%Si alloy is composed of coarse α-Al dendrites and flaked eutectic Si, which leads to premature cracking caused by tensile stress concentration. When 0.5 wt.% Al–TiCCe master alloy was added, it can be clearly observed from Figure 12b that the area of cleavage planes significantly decreases and the number of dimples increases on the fracture surfaces due to the refinement of α-Al dendrites and the eutectic structure. As can be seen from Figure 12c, when 1.0 wt.% Al–TiCCe master alloy was added, a large number of dimples and torn ridges were observed. On the fracture surface of Al–7%Si alloy with addition of 1.5 wt.% master alloy, the ductile fracture type is found. Owing to the reduction of the size and the passivation of the sharp angle of most of the eutectic Si, the cleavage effect of the eutectic Si on the aluminum substrate is reduced. In the unrefined hypoeutectic Al–7%Si alloy, the dendritic α-Al is very coarse and the secondary dendrite is abundant and the eutectic silicon is distributed in the α-Al matrix as a long needle. Under the action of tensile stress, stress concentration and crack initiation are easy to occur at the dendritic tip and at the sharp corner of eutectic silicon, which makes the alloy material exhibit poor properties.45,46 After adding 1.5 wt.% Al–TiCCe master alloy, not only the α-Al phase is refined, but also the size is obviously reduced and the angle is passivated, while the long acicular eutectic silicon also becomes spherical and granular. As a result, the slip distance of dislocation is shortened, the number of dislocations accumulated in front of obstacles is smaller, and the stress concentration at grain boundaries is smaller. For this reason, it is necessary to increase the applied stress in order to start the source of dislocation in the crystal. Therefore, the alloy materials with better refining and modification effect have difficulty in crack initiation, and show better strength and toughness.46 However, as the Al–TiCCe master alloy content was increased to 2.0 wt.%, the fracture was made up of cleavage surfaces and dimples, as shown in Figure 12e. This is due to the increase in the size of α-Al phase and eutectic phase in the alloy, which has the effect of splitting the matrix, which seriously affects the mechanical properties of the hypoeutectic Al–7%Si alloy.
Figure 12

Fractographs of the tensile samples of Al-7Si alloy with various contents of Al–TiCCe master alloy: (a) unmodified; (b) 0.5 wt.%; (c) 1.0 wt.%; (d) 1.5 wt.%; and (e) 2.0 wt.%.

The above results show that Al–TiCCe is an excellent master alloy, which can not only refine α-Al dendrites in Al–7%Si alloy, but also modify eutectic Si, thus improving the tensile strength and elongation of Al–7%Si alloy. By increasing the content of Ce in Al–TiCCe master alloy, a new type of Al–TiCCe master alloy with better properties may be prepared. Therefore, a new method of preparing Al–TiCCe master alloy by adding CeO2 in the thermal explosion reaction of pure aluminum is proposed, which provides the possibility for industrial application.

Conclusions

A new type of Al–TiCCe master alloy was prepared, and its effect on the microstructure and mechanical properties of hypoeutectic Al–7%Si alloy was studied. The following conclusions were drawn:
  1. 1.

    When the amount of CeO2 is 4%, the synthesis temperature is 820 °C, and the holding time is 10–15 min, the new type of Al–TiCCe master alloy can be prepared in the thermal explosion reaction of pure molten aluminum.

     
  2. 2.

    With increasing Al–TiCCe master alloy content, the secondary dendritic spacing and eutectic Si size of hypoeutectic Al–7%Si alloy first decreased and then increased. Addition of 1.5 wt.% Al–TiCCe master alloy not only refined the α-Al dendrites from coarse to fine equiaxed grains, but also modified eutectic Si from coarse needle flakes to fibrous and small granules.

     
  3. 3.

    With increasing Al–TiCCe master alloy content, the tensile strength and elongation first increased and then decreased. When 1.5 wt.% Al–TiCCe master alloy was added, the tensile strength and elongation reached their peaks, 248 MPa and 6.7%, an increase of 59% and 56%, respectively.

     

Notes

Acknowledgements

We would like to thank LetPub (www.letpub.com) for providing linguistic assistance during the preparation of this manuscript. This research was financially supported by the National Natural Science Foundation of China (Nos. 51661021; 51665033). The authors would like to acknowledge the financial support of the Natural Science Foundation of Gansu Province in China (No. 1606RJZA161) and Gansu key research and development program (No. 18YF1GA061).

Compliance with Ethical Standards

Conflict of interest

The authors declare no conflicts of interest.

References

  1. 1.
    J. Rakhmonov, G. Timelli, F. Bonollo, L. Arnberg, Influence of grain refiner addition on the precipitation of Fe-rich phases in secondary AlSi7Cu3Mg alloys. Int. J. Metalcast. 11, 294–304 (2017)CrossRefGoogle Scholar
  2. 2.
    D.G. Mallapur, K. Rajendra Udupa, S.A. Kori, Studies on the influence of grain refining and modification on microstructure and mechanical properties of forged A356 alloy. Mater. Sci. Eng. A 528, 4747–4752 (2011)CrossRefGoogle Scholar
  3. 3.
    S.L. Lee, Y.C. Cheng, W.C. Chen, C.K. Lee, A.H. Tan, Effects of strontium and heat treatment on the wear-corrosion property of Al–7Si–0.3Mg alloy. Mater. Chem. Phys. 135, 503–509 (2012)CrossRefGoogle Scholar
  4. 4.
    Q.L. Li, F.B. Li, T.D. Xia, Y.F. Lan, Y.S. Jian, F. Tao, Effects of in situ γ-Al2O3 particles and heat treatment on the microstructure and mechanical properties of A356 aluminium alloy. J. Alloys Compd. 627, 352–358 (2015)CrossRefGoogle Scholar
  5. 5.
    G.K. Sigworth, Understanding quality in aluminum castings. Int. J. Metalcast. 5, 7–22 (2011)CrossRefGoogle Scholar
  6. 6.
    G.K. Sigworth, Fundamentals of solidification in aluminum castings. Int. J. Metalcast. 8, 7–20 (2014)CrossRefGoogle Scholar
  7. 7.
    J.H. Li, M.Z. Zarif, M. Albu, B.J. McKay, F. Hofer, P. Schumacher, Nucleation kinetics of entrained eutectic Si in Al-5Si alloys. Acta Mater. 72, 80–98 (2014)CrossRefGoogle Scholar
  8. 8.
    K.G. Basavakumar, P.G. Mukunda, M. Chakraborty, Influence of grain refinement and modification on microstructure and mechanical properties of Al-7Si and Al-7Si-2.5Cu cast alloys. Mater. Charact. 59, 283–289 (2008)CrossRefGoogle Scholar
  9. 9.
    G.K. Sigworth, The modification of Al-Si casting alloys: important practical and theoretical aspects. Int. J. Metalcast. 2, 19–40 (2008)CrossRefGoogle Scholar
  10. 10.
    S.D. McDonald, K. Nogita, A.K. Dahle, Eutectic nucleation in Al-Si alloys. Acta Mater. 52, 4273–4280 (2004)CrossRefGoogle Scholar
  11. 11.
    A.K. Dahle, K. Nogita, S.D. McDonald, C. Dinnis, L. Lu, Eutectic modification and microstructure development in Al-Si Alloys. Mater. Sci. Eng. A 413–414, 243–248 (2005)CrossRefGoogle Scholar
  12. 12.
    O. Uzun, F. Yılmaz, U. Ko¨lemen, N. Basman, Sb effect on micro structural and mechanical properties of rapidly solidified Al-12Si alloy. J. Alloys Compd. 509, 21–26 (2011)CrossRefGoogle Scholar
  13. 13.
    C.X. Xu, L.P. Liang, B.F. Lu, J.S. Zhang, L. Wei, Effect of La on microstructure and grain–refining performance of Al-Ti-C grain refiner. J. Rare Earths 24, 596–601 (2006)CrossRefGoogle Scholar
  14. 14.
    T. Lu, Y. Pan, J.L. Wu, S.W. Shi, Y. Chen, Effects of La addition on the microstructure and tensile properties of Al-Si-Cu-Mg casting alloys. Int. J. Miner. Metal. Mater. 22, 405–410 (2015)CrossRefGoogle Scholar
  15. 15.
    M.G. Mahmoud, E.M. Elgallad, M.F. Ibrahim, F.H. Samuel, Effect of rare earth metals on porosity formation in A356 alloy. Int. J. Metalcast. 12, 251–265 (2018)CrossRefGoogle Scholar
  16. 16.
    D. Yao, F. Qiu, Q. Jiang, Y. Li, L. Arnberg, Effect of lanthanum on grain refinement of casting aluminum-copper alloy. Int. J. Metalcast. 7, 49–54 (2013)CrossRefGoogle Scholar
  17. 17.
    B. Li, H.W. Wang, J.C. Jie, Z.J. Wei, Microstructure evolution and modification mechanism of the ytterbium modified Al-7.5%Si-0.45%Mg alloys. J. Alloys Compd. 509, 3387–3392 (2011)CrossRefGoogle Scholar
  18. 18.
    Q.L. Li, T.D. Xia, Y.F. Lan, W.J. Zhao, L. Fan, P.F. Li, Effect of rare earth cerium addition on the microstructure and tensile properties of hypereutectic Al-20%Si alloy. J. Alloys Compd. 562, 25–32 (2013)CrossRefGoogle Scholar
  19. 19.
    X.F. Liu, Z.Q. Wang, Z.G. Zhang, The relationship between microstructures and refining performances of Al-Ti-C master alloys. Mater. Sci. Eng. A 332, 70–74 (2002)CrossRefGoogle Scholar
  20. 20.
    G.K. Sigworth, T.A. Kuhn, Grain refinement of aluminum casting alloys. Int. J. Metalcast. 1, 31–40 (2007)CrossRefGoogle Scholar
  21. 21.
    Y.L. Li, H.K. Feng, F.R. Cao, Y.B. Chen, L.Y. Gong, Effect of high density ultrasonic on the microstructure and refining property of Al–5Ti–0.25C grain refiner alloy. Mater. Sci. Eng. A 487, 518–523 (2008)CrossRefGoogle Scholar
  22. 22.
    G.S. Kumar, B.S. Murty, M. Chakraborty, Development of Al–Ti–C grain refiners and study of their grain refining efficiency on Al and Al–7Si alloy. J. Alloys Compd. 396, 143–150 (2005)CrossRefGoogle Scholar
  23. 23.
    V.H. López, A. Scoles, A.R. Kennedy, The thermal stability of TiC particles in an Al-7wt.%Si alloy. Mater. Sci. Eng. A 356, 316–325 (2003)CrossRefGoogle Scholar
  24. 24.
    J.H. Wu, H.L. Zhao, J.X. Zhou, W.H. Li, J.W. Wang, L.L. Zhang, Effects of Al-Ti-B-Sr master alloy on the microstructure and mechanical properties of A356 alloy. Mater. Sci. Forum 898, 131–136 (2017)CrossRefGoogle Scholar
  25. 25.
    A.K. Prasada Rao, K. Das, B.S. Murty, M. Chakraborty. Microstructures and wear behavior of hypoeutectic Al-Si alloy (LM25) grain refined and modified with Al-Ti-C-Sr master alloy. Wear 261, 133–139 (2006)CrossRefGoogle Scholar
  26. 26.
    H.L. Zhao, J.S. Yue, Y. Gao, K.R. Weng, Grain and dendrite refinement of A356 alloy with Al-Ti-C-RE master alloy. Rare Met. 32, 12–17 (2013)CrossRefGoogle Scholar
  27. 27.
    C. Xu, W.L. Xiao, W.T. Zhao, W.H. Wang, H. Shuji, Y. Hiroshi, C.L. Ma, Microstructure and formation mechanism of grain-refining particles in Al-Ti-C-RE grain refiners. J. Rare Earths 33, 553–560 (2015)CrossRefGoogle Scholar
  28. 28.
    L. Lu, A.K. Dahle, Effect of combined additions of Sr and Al-Ti-B grain refiners in hypoeutectic Al-Si foundry alloys. Mater. Sci. Eng. A 435–436, 288–296 (2006)CrossRefGoogle Scholar
  29. 29.
    X.G. Qi, X.F. Bian, Y.H. Wang, Grain refinement and modification effects of Al-Ti-B and Al-5%Sr master alloys on the wheel aluminum alloy. Foundry 49, 321–326 (2000)Google Scholar
  30. 30.
    Y.M. Liu, B.F. Xu, X. Cai, L.H. Li, Q.L. Chen, The preparation of in situ TiC/Al composite by additive CeO2. J. Shanghai Jiaotong Univ. 38, 1122–1125 (2004)Google Scholar
  31. 31.
    Q.L. Wu, Y.S. Sun, F. Xue, J. Zhuo, Effect of CeO2 addition on microstructure and properties of in situ TiC strengthened steel. J. Chin. Rare Earth Soc. 26, 92–96 (2008)Google Scholar
  32. 32.
    L.D. Wang, Z.L. Wei, X.B. Yang, D.Y. Zhu, X. Chen, Y.L. Chen, L.H. Hong, Q.J. Li, Thermodynamic analysis of Al-Ti-C-RE prepared by rare Earth oxide Ce2O3. Trans. Nonferr. Met. Soc. China 23, 2928–2935 (2013)Google Scholar
  33. 33.
    W.W. Ding, C. Xu, H.X. Zhang, W.J. Zhao, T.B. Guo, T.D. Xia, Effect of Al-5Ti-0.62C-0.2Ce master alloy on the microstructure and tensile properties of commercial pure Al and hypoeutectic Al-8Si alloy. Metals 7, 227–240 (2017)CrossRefGoogle Scholar
  34. 34.
    W.W. Ding, X.Y. Zhang, W.J. Zhao, T.D. Xia, Microstructure of Al-5Ti-0.6C-1Ce master alloy and its grain-refining performance. Int. J. Mater. Res. 106, 1240–1243 (2015)CrossRefGoogle Scholar
  35. 35.
    Q. Ma, Heterogeneous nucleation on potent spherical substrates during solidification. Acta Mater. 55, 943–953 (2007)CrossRefGoogle Scholar
  36. 36.
    A.L. Greer, A.M. Bunn, A. Tronche, P.V. Evans, D.J. Bristow, Modelling of inoculation of metallic melts: application to grain refinement of aluminium by Al-Ti-B. Acta Mater. 48, 2823–2835 (2000)CrossRefGoogle Scholar
  37. 37.
    C. Small, P. Prangnell, F. Hayes, A. Hardman, Microstructure and grain refining efficiency of TiC particles in Al-Ti-C grain refining master alloys, in ICAA-6: 6th International Conference on Aluminium Alloys, Toyohashi, Japan (1998), p. 213Google Scholar
  38. 38.
    A. Banerji, W. Reif, Development of Al-Ti-C grain refiners containing TiC. Metall. Trans. A 17, 2127–2137 (1986)CrossRefGoogle Scholar
  39. 39.
    T.D. Xia, W.W. Ding, W.J. Zhao, Effect of distribution of TiC in aluminum matrix in the presence of solute TiAl3 and nucleation mechanism of Al-Ti-C. Trans. Nonferr. Met. Soc. China 19, 1948–1955 (2009)Google Scholar
  40. 40.
    W.W. Ding, W.J. Zhao, T.D. Xia, Grain refining action of Al-5Ti-C and Al-TiC master alloys with Al-5Ti master alloy addition for commercial purity aluminum. Int. J. Cast. Metal. Res. 27, 187–192 (2014)CrossRefGoogle Scholar
  41. 41.
    S.H. Wang, Z.F. Wang, X.Y. Fan, X.F. Jia, Y. Zhao, L. Zhang, Effect of different RE Ce master alloy on microstructure of A356 alloy. China Foundry Mach. Technol. 4, 7–11 (2010)Google Scholar
  42. 42.
    G.K. Sigworth, M.M. Guzowaski, Grain refining of hypo-eutectic Al-Si alloys. AFS Trans. 93, 907–912 (1985)Google Scholar
  43. 43.
    D. Qiu, J.A. Taylor, M.X. Zhang, P.M. Kelly, A mechanism for the poisoning effect of silicon on the grain refinement of Al-Si alloys. Acta Mater. 55, 1447–1456 (2007)CrossRefGoogle Scholar
  44. 44.
    P.T. Li, S.D. Liu, L.L. Zhang, X.F. Liu, Grain refinement of A356 alloy by Al-Ti-B-C master alloy and its effect on mechanical properties. Mater. Design. 47, 522–528 (2013)CrossRefGoogle Scholar
  45. 45.
    Q.L. Li, B.Q. Li, J.B. Li, T.D. Xia, Y.F. Lan, T.B. Guo, Effects of the addition of Mg on the microstructure and mechanical properties of hypoeutectic Al-7%Si alloy. Int. J. Metalcast. 11, 823–830 (2017)CrossRefGoogle Scholar
  46. 46.
    X.S. Li, A.H. Cai, Y. Luo, Influence of B refinement on mechanical properties and fracture surfaces of hypoeutectic Al–Si alloy. J. Hunan Inst. Sci. Technol. 22, 34–38 (2009)Google Scholar

Copyright information

© American Foundry Society 2018

Authors and Affiliations

  1. 1.State Key Laboratory of Advanced Processing and Recycling of Nonferrous MetalsLanzhouChina
  2. 2.School of Materials Science and EngineeringLanzhou University of TechnologyLanzhouChina

Personalised recommendations