Study of microstructure and microhardness behavior of SS321/HK31A dissimilar joint using laser welding

Abstract

In this study, metallurgical behavior and microhardness of dissimilar butt joints of SS321 and HK60A Mg sheets using change of laser power was investigated. The effects of power, heat input and cooling rate during laser welding on weld appearance and hardness were studied. Furthermore, microstructure analysis was used to examine the metallurgical behavior and microhardness of the weld. Results showed that due to select of Gaussian beam for welding and the much lower melting point of HK31A compared to SS321, its resistance to melting was lower and without severe curvature, melting occurred from the top to the bottom of HK31/HK31 joints. On the other hand, in SS321/SS321 joints, a severe curvature was observed due to its resistance to melting in the middle of the weld. It was observed that the only effective factor in the temperature difference of the weld pool is heat input (input power). With an 11 % increase in heat input, the temperature of the weld pool for H1 sample was 8 % lower than that of H2 sample. Also, for sample A1, it was 0.9 % lower than sample A2. Since the Bessel function value was 4.07 for H1 and H2 samples and 0.95 for A1 and A2 samples, the melt pool temperature values of H1 and H2 samples were 85 % lower than the melt pool temperature of A1 and A2 samples. It should be noted that microhardness of samples decreased by increasing power and decreasing cooling rate.