Abstract
The present study aims to investigate the effect of microstructure and texture on mechanical properties of resistance spot welding of high strength steel 22MnB5 and 5A06 aluminium alloy as a function of welding parameters. The pseudo-nugget zones (NZs) at the steel side have undergone full recrystallisation with a fine-grained ferrite structure containing a small amount of retained austenite and a high hardness of approximately 500 HV, which is a 35% increase in hardness compared to the base material (BM) with fine lath martensitic structure. The NZs at the Al side contain both a recrystallisation texture and shear texture. Higher tensile shear strength with increasing weld time could be linked to the random texture at the Al side. The highest tensile shear strength was achieved at an intermetallic layer thickness of 4 mm.
Highlights
In recent years, with the rapid development of automotive industry, there is an increasing demanding of automobile safety and comfort, energy saving and environmental protection
A study of resistance spot welded (RSWed) Al and steel by Oikawa et al [6] reported that the thickness of the intermetallic compound (IMC) layer increased with increasing welding current, in addition, Qiu et al [7,8,9] found that tensile shear strength decreased with increasing welding current and the tensile shear strength decreased with increasing thickness of the IMC layers [10,11]
The steel base material (BM) (Figure 3a) showed a typical microstructure of hot stamped steel with ultimate tensile strength larger than 1500 MPa consisting of coarse-lathed martensite within prior austenite grains, at the steel side, the heat affected zone (HAZ) retained the lath martensite and a new type of grain structure other than the lath martensite were developed in the HAZ, and grains were significantly refined in the nugget zones (NZs) with an equiaxed microstructure
Summary
With the rapid development of automotive industry, there is an increasing demanding of automobile safety and comfort, energy saving and environmental protection. A study of resistance spot welded (RSWed) Al and steel by Oikawa et al [6] reported that the thickness of the IMC layer increased with increasing welding current, in addition, Qiu et al [7,8,9] found that tensile shear strength decreased with increasing welding current and the tensile shear strength decreased with increasing thickness of the IMC layers [10,11]. A study of RSWed dissimilar Al and steel by Shin et al [14] reported that a highly brittle thinner IMC layer with a thickness of 2.39 μm had a higher strength. The tensile shear strength of the welded spots of steel and aluminum alloy was not affected by the IMC layer with a thickness of 4 μm [13,15]. For RSWed aluminium and high strength steel, the high strength steel side with initial martensitic structure was not understood, and the effect of texture of aluminium and steel on mechanical properties has not been reported before, the present paper aims to investigate microstructure, texture evolution and mechanical properties of RSWed aluminium and high strength steel with initial martensitic structure
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