Weld properties and residual stresses of VPPA Al welds at varying welding positions

Abstract

The micro-structure and residual stresses of VPPA welds at varying welding positions still lack systematic research. To clarify the effects of gravity on Al weld performance, 7 welding positions (from vertical-up welding to horizontal welding) were used to investigate the evolution of microstructure, mechanical properties and residual stresses. The results showed that both micro-structure and residual stresses of the welded joints in non-vertical up welding were asymmetric while those in vertical up welding were symmetric. The grain size on the upper side of the welded joints increased from about 66.9 µm for vertical up welding to 113.9 µm for horizontal welding. Furthermore, though lots of tear ridges and dimples appeared in all the fracture surfaces, which showed ductile fracture, all fractures for non-vertical up welding appeared on the upper side of the weld. The tensile strength from vertical up welding to horizontal welding decreased from 352.8 MPa to 319.8 MPa. In this paper, the formation mechanisms and underlying cause of the asymmetric residual stresses and mechanical properties in non-vertical up welding have been analysed and discussed.

Keywords

• Microstructure
• Mechanical properties
• Residual stress
• Grain size
• Gravity effects