Restraint Stress and Plastic Deformation in Multi-Layer Welding of Aluminum Alloy

Abstract

In this paper, the mechanisms of restraint force and bending moment as well as transverse distortions in multi-pass TIG welding of aluminum alloy are experimentally studied using H-type restrained V-groove joints, and the discussions emphasize plastic deformation in the weld. The main results are as follows.
1) Cooling effect of the shield gas causes a sharp drop in peak temperature of weld thermal cycle at top surface layer of the weld zone and consequently temporary fluctuation of the transient bending moment.
2) The basic mechanisms of restraint stress and distortions in the weld are generally the same as in welding thick steel plate.
3) In welding each pass, the transverse shrinkage by plastic deformation grows up at vicinity of the weld metal under restraint compressive stress during heating process, and then decreases by elongation under restraint tensile stress during cooling process with a consequent shrinkage at room temperature. The tensile plastic strain occurs in a wide area of the base plate as well as the weld zone, and the transient tensile stress at boundary of the area reaches the value of yield stress of the base metal at a temperature during cooling process. Both magnitude of the plastic strain and extent of the plastic zone increase with increasing built-up passes.