Effects of Sc on laser hot-wire welding performance of 7075 aluminum alloy

Abstract

In order to clarify the effects of Sc modification on laser hot-wire welding performance of 7075 high strength aluminum alloys, the changing rules of weld formation, microstructure, element loss, mechanical performances and pores of weld joints were investigated during laser fusion welding, laser hot-wire welding and Sc-modified laser hot-wire welding. Comparing with laser fusion welding, the filler wire in laser hot-wire welding brought welding material and hot wire energy, resulting in better weld formation and sufficient fused weld joint. In laser hot-wire welding, tensile strength and elongation of weld joint were enhanced, element loss of weld joint was dramatically reduced and weld pore was reduced slightly. However, grains in fusion zone were relatively coarse, which caused lower microhardness in laser hot-wire welding. In Sc modified laser hot-wire welding, Sc modification led to smooth and continuous weld joint. During solidification of weld joints, Sc could combine with base metal to form Sc-containing alloy phase, which could lead to the formation of refined and equiaxed grains, thereby enhancing the yield strength of microstructure and increasing the microhardness, tensile strength and elongation of weld joint. In addition, Sc modification could increase the fluidity of molten pool, which thus promoted the escape of bubbles from the molten pool and hindered the formation of weld pores.