Study on Gas Bulging Forming and Contradictive Cooling Bonding of AZ31/Al7475 Bimetal Composite Tube

Mg/Al bimetallic tubes can give full play to the excellent properties of magnesium alloys and aluminum alloys, such as light weight, high strength and good corrosion resistance. In this study, gas bulging forming and contradictive cooling bonding process was used to form AZ31/Al7475 hexagonal section composite tubes and showed a good result. In addition, the finite element analysis method was utilized to simulate the process and optimize the forming parameters. The results show that the process could be divided into four stages: free bulging stage, sidewall sticking stage, fillet filling stage and contradictive cooling stage. The maximum thinning rate and fillet radius of AZ31/Al7475 composite tube were 10.60% and 7.00 mm, respectively, at 450 °C, 6 MPa, and 600-720 s. And the interface between the inner and outer layers was closely combined. The bonding force of the rounded corner part of the forming part was 2.04, and 2.30 MPa for the straight wall part. The experimental value of the binding force was about 28% higher than the maximum theoretical value.