Effect of process parameters on performances of TWIP steel/Al alloy dissimilar metals butt joints by laser offset welding

Abstract

In this paper, butt joints of twinning-induced plasticity (TWIP) steel and aluminum alloy dissimilar metals were carried out by the laser offset welding method, and the amount of the aluminum alloy that melted was controlled by adjusting the offset distance of the laser beam spot. The aim of this study was to regulate the influence of the intermetallic compounds (IMCs) layer thickness, crystal structure and crack defects on the tensile strength of the welded joint. The tensile strength of the welded joint was obviously improved by adjusting the welding process parameters without adding any alloying elements. The results demonstrated that the crack initiated at the junction between the aluminum base metal and the weld seam and propagated along with the interface. The increase in the recrystallized fraction was beneficial to improve the tensile strength of the joint. The tensile strength of welded joints with more low-angle grain boundaries was lower. The smaller the thickness of the IMCs layer was, the higher the welded joint strength was. The optimized welding process parameters were as follows: d = 0.2 mm, P = 900 W, V = 15 mm/s and △f = −2 mm in the present study, and the tensile strength of the joint reached 155 MPa. This study provides a theoretical basis for solving the welding cracking problem of steel/aluminum heterojunctions without additional interlayer material and so as to improve the strength of the steel/aluminum laser welded joint.