Abstract:The residual stress on surface of variable polarity plasma arc (VPPA) weldedS5A06 aluminium alloy sampleSwas measured by synchrotron radiation X-ray diffraction, and the distribution of residual stress on the surface of the sample was obtained in this paper. The generation and evolution mechanisms of weld zone, heat affected zone, base metal area were analyzed in combination with metallurgical structureSobservation, EBSD and microhardness tester methods. The results show that the weld zone of VPPA welded 5A06 plate shows coarse grainS, the grains in the heat affected zone are small, the residual stress presents an "M" shape: the weld zone is compressive stress, and the heat affected zone is tensile stress; There is a maximum tensile stress of 75.79 MPa and a maximum compressive stress of 159.34 MPa in the direction vertical weld (TD) and a maximum tensile stress of 132.33 MPa and a maximum compressive stress of 89.38 MPa in the direction parallel to the weld (LD). Compared with the trend of the residual stress measured by traditional X-ray instrument, the distribution trend of the residual stress of the synchrotron radiation diffraction measurement is more consistent with the variation trend of the microhardness of the sample in different welding areas. The experimental results show that the residual stress data of synchrotron radiation X-ray diffraction measurement has better consistency than the traditional X-ray instrument.