Study on the mechanism of TiB₂ on the microstructure properties of 5356 aluminum alloy welds

The addition of heteronucleating metamorphic agent is the main way to obtain fine grain tissue. In order to study the effect of TiB₂ particles on the microstructure properties of 5356 aluminum alloy welds, Al-Mg welded joints were fabricated by powder-cold metal transition (CMT) process, and the effects of TiB₂ particles on weld structure and mechanical properties were analyzed. The results showed that the addition of TiB₂ particles could significantly refine the grain structure of the weld, weaken the grain growth and texture characteristics, increase the proportion of large-angle grain boundaries, reduce the size of the second phase and promote its diffusion distributionAs a heterogeneous nucleation core, TiB₂ particles promote the precipitation of the second phase of Al₃Mg₂, reduce its size, make its distribution more uniform, and significantly reduce the size of the weld structure. Compared with the weld specimen without particle addition, the addition of TiB₂ with 0.73% mass fraction reduced the average grain size from 96.7 μm to 64.2 μm, increased the tensile strength from 202.4 MPa to 216.7 MPa, and increased the elongation from 19.8% to 25.5%. The average hardness of the weld increased with the increase of TiB₂ content, and the hardness of TiB₂ increased from 65.18 HV to 73.97 HV.The fracture mechanism of weld metal is ductile fracture.