アルミニウムおよびその合金のMIG溶接における被包ガスへの窒素および酸素の添加について

Abstract

In this study, the effects of nitrogen an/or oxygen added to shielding gas on the weldability of aluminum alloys were investigated.Test materials were welded by manual and machine MIG welding equipments under various welding conditions.Weldability was evaluated by various properties of welds, such as appearance, shape and depth of penetration, porosities, structures, mechanical properties and others.The results were as follows:(1) Addition of nitrogen to argon gas was apt to form brown scales on bead surface of aluminum and its alloys, particularly of Al-Mg alloys, but the bead shape was scarcely disturbed by the addition of up to 10% nitrogen.It increased the depth of penetration and improved the tensile strength with refined structures of weld metal. Furthermore, it reduced the porosities in commercially pure aluminum welds, though it was not always effective for reducing them in aluminum alloys, particularly in alloys containing magnesium considerably.(2) Addition of oxygen to argon gas was apt to cause the puckering phenomenon, but that of up to 5% oxygen gave a comparatively excellent bead shape with no puckering.It increased the depth of penetration and produced the welds with few porosities in both aluminum and its alloys.(3) Simultaneous addition of nitrogen and oxygen to argon gas disturbed the bead shape with remarkable scales.It tended to form inclusions in welds, while it increased considerably the depth of penetration and occasionally decreased the porosities.(4) Consequently, it was considered that addition of nitrogen gas up to 10% or that of oxygen gas up to 5% was effective in practical applications, but simultaneous addition of them was not desirable.