Correlating microstructural features with improved wear and corrosion resistance of laser surface remelted A356 alloy at different scanning speeds

Abstract

In this work, two scanning speeds (2 mm/s and 8 mm/s) were employed to remelt the surface of an A356 cast Al alloy by a pulsed laser at 300 W, with microstructural features of the laser-remelted surface layers well characterized and correlated with their wear/corrosion resistance. Through high-quality microstructure characterizations, it is found that the as-received A356 alloy is comprised of coarse α-Al dendrites and interdendritic AlSi eutectics. After laser surface remelting (LSR) at both speeds, microstructure homogeneity is greatly improved due to the remarkable refinement of the dendrites and interdendrites. Hardness and wear tests show that surface hardness and wear rate of the 2 mm/s specimen are 71.6 ± 0.6 HV and 1.1 × 10−3 mm3·N−1·m−1, while those of the 8 mm/s specimen are 67.2 ± 1.1 HV and 1.7 × 10−3 mm3·N−1·m−1, respectively, markedly improved compared to the substrate (55.3 ± 0.5 HV and 2.8 × 10−3 mm3·N−1·m−1). Electrochemical test results reveal that self-corrosion potential (Ecorr) and current (Icorr) of the 2 mm/s specimen are −0.82 V and 9.5 × 10−7 μA, while those of the 8 mm/s specimen are −0.89 V and 1.8 × 10−6 μA, respectively. After comparing with the substrate (−0.95 V and 4.3 × 10−6 μA), the corrosion resistance of both the LSRed specimens is confirmed to be significantly enhanced. Comprehensive analyses reveal that after the LSR the simultaneously increased wear/corrosion resistance can be related to the largely homogenized microstructure, the enhanced supersaturation of Si in α-Al, and the refinement and redistribution of AlSi eutectics in the remelted layer.