Dissimilar Laser Welding/Brazing of 5754 Aluminum Alloy to DP 980 Steel: Mechanical Properties and Interfacial Microstructure
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A diode laser welding/brazing technique was used for lap joining of 5754 aluminum alloy to DP 980 steel with Al-Si filler metal. The correlation between joint interfacial microstructure, wettability of filler metal, and mechanical properties was systematically investigated. At low laser power (1.4 kW), a layer of intermetallic compounds, composed of θ-Fe(Al,Si)3 and τ 5 -Al7.2Fe1.8Si, was observed at the interface between fusion zone and steel. Because of the poor wettability of filler metal on the steel substrate, the joint strength was very low and the joint failed at the FZ/steel interface. When medium laser power (2.0 kW) was applied, the wettability of filler metal was enhanced, which improved the joint strength and led to FZ failure. With further increase of laser power to 2.6 kW, apart from θ and τ 5, a new hard and brittle η-Fe2(Al,Si)5 IMC with microcracks was generated at the FZ/steel interface. The formation of η significantly degraded the joint strength. The failure mode changed back to interfacial failure.
KeywordsLaser Power Filler Metal High Laser Power Joint Strength DP980 Steel
Financial support of State Scholarship Fund of China (Grant No. 201306820002) and the National Natural Science Foundation of China (No. 51265035) is gratefully acknowledged. The authors would like to thank Dr. A.M. Nasiri and PhD candidates H. Huang, D.C. Saha, and D. Xu from Centre for Advanced Materials Joining, University of Waterloo, for valuable discussions. The authors thank Dr. Yuquan Ding from the Materials Science and Engineering Group, University of Waterloo, for the help with SEM, EDS, and nanohardness operations. The TEM research was performed at the Canadian Centre for Electron Microscopy at McMaster University, which is supported by NSERC and other government agencies.
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