Innovative heterostructure enhance mechanical strength and corrosion resistance in A356/6061 dissimilar aluminum alloy MIG welded joints

Abstract

Designing heterostructure (HS) is an effective approach to enhancing the metallic materials property. In this study, ultrasonic impact treatment (UIT) is used to construct gradient HS and bionic HS on the dissimilar Al alloy joints surface. The results indicate that after UIT, the size of grains and intermetallic compounds is refined and the dislocation density is increased, leading in a surface hardness increase of more than 50 %. After immersion in 3.5 wt% NaCl solution for 7 days, the strength and toughness of the as-welded sample decreased significantly, whereas the welded joint with HS maintained high strength with only a slight loss in toughness. Due to the combined effects of multiple strengthening mechanisms, the bionic HS welded joint has the best tensile properties under pre-corrosion conditions. Compared to the as-welded samples, the tensile strength, yield strength and elongation of the bionic HS welded joint are increased by 39.7 %, 57.3 % and 4 %, respectively. Additionally, UIT formed a high proportion of low angle grain boundaries and a compressive residual stress layer with a maximum of −194 ± 3 MPa, promoting the stable growth of dense passivation film, thereby enhancing the intergranular corrosion resistance and electrochemical corrosion property of the welded joint.