7A52 aluminum alloy VPPA-MIG hybrid welding residual stress testing based on elastic modulus variation

A residual stress testing system based on hole-drilling method was designed by virtual instrument and NI data acquisition card to analyze the welding residual stress distribution for 7A52 aluminum alloyplates after the process of VPPA-MIG hybrid welding. To reduce the impact of elastic modulus error on the final measurement results, the elastic modulus is derived from curve that is fit to data measured in different hybrid welded joint areas. The experiment of VPPA-MIG welding residual stress measurement was carried out on 10 mm thick 7A52 aluminum alloy plates. The results show that the distribution of residual stresses on two sides of weld is basically symmetrical along the weld center. Maximum tensile stresses exist in the fusion zone, and the maximum transverse residual stress σ_y and the maximum longitudinal residual stress σ_x are 118 and 223 MPa, respectively. From fusion zone to heat affected zone, residual stresses are all tensile stresses, which become smaller gradually and are higher than the residual stresses in the weld center. Compared with the result of MIG welding, the maximum transverse residual stress and the maximum longitudinal residual stress of VPPA-MIG hybrid welding are higher, but the high-stress area of VPPA-MIG hybrid welding are narrower.