Abstract
An experimental study of the heat treatment of 359-SiC 20p composite and its base alloy was made to determine the strength-ductility characteristics under varying conditions of heat treatment. Microstructural observations revealed that addition of the SiCp reinforcement to the base alloy produced a more uniform and refined interdendritic microstructure compared to the latter. The tensile data obtained was analysed in terms of the theoretical models existing in the composite literature. Ultimate tensile strength (UTS)-log elongation relationships were obtained to test the applicability of the quality index parameter,Q, to the present composite. From this analysis, it was found that all data points in the ageing temperature range 140–210 °C could be represented by a single line (cf. two lines in the case of 359 alloy), indicating the important fact that the tensile properties of this composite can be predicted/determined over the entire temperature range. The presence of the SiC particles was seen to accelerate the Mg2Si precipitation kinetics, but not to alter it. Fracture mechanisms were determined from both the fracture surfaces and their longitudinal sections beneath the fracture surface, employing both optical and scanning electron microscopy.
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Abbreviations
- a :
-
Particle diameter
- b :
-
Burger's vector
- b ii :
-
Numerical constant relating 〈P Eii 〉m andP A33
- E c :
-
Young's modulus of the composite
- E m :
-
Young's modulus of the matrix
- E p :
-
Young's modulus of SiC particles
- El:
-
Elongation (%)
- f p :
-
SiC volume fraction
- P A33 :
-
Applied stress
- 〈P E ii 〉:
-
Long range back stress developed by elastic misfit
- ΔP Fm :
-
Change in matrix flow stress
- <P Pii >m :
-
Back stresses due to plastic deformation
- P psc :
-
Proof strain of a composite
- q ii :
-
Plastic misfit
- Q :
-
Quality index
- R :
-
Statistical correlation coefficient
- RE:
-
Rockwell E hardness value
- S :
-
SiC particle aspect ratio
- S c :
-
Critical aspect ratio for the SiC particles
- UTS:
-
Ultimate tensile strength of the alloy or composite
- YS:
-
Yield strength of the alloy or composite
- α:
-
Critical misfit strain
- γ:
-
Constant, 1.25 for aluminum alloys
- ɛ:
-
Plastic strain
- ɛps :
-
Plastic strain at whichP psc is required
- \(\dot \theta \) :
-
Work hardening rate at a given plastic strain
- \(\ddot \theta \) :
-
Work hardening rate as a function of total strain
- μ:
-
Shear modulus
- \(\overline \rho \) :
-
Dislocation density
- σ Oc :
-
Yield stress of the composite
- ΔσCTE :
-
Increase in yield stress due to coefficient of thermal expansion (CTE)
- σ Om :
-
Yield stress of the matrix
- σp :
-
Particle strength
- τi :
-
Interfacial shear strength
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Samuel, A.M., Samuel, F.H. Analysis of the tensile properties and fractography of as-cast and heat treated 359-SiC-20p composite. J Mater Sci 30, 3098–3110 (1995). https://doi.org/10.1007/BF01209223
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DOI: https://doi.org/10.1007/BF01209223