Effects of heat inputs on solidified structures of aluminum alloy welds

Abstract

These studies were made on the morphology of solidified structures in aluminum alloy welds. Experiments were conducted to investigate the effects of heat inputs on grain-structures, dendrite cell size, distributions of solutes and other behaviors of 99.5%Al, Al-4.5%Mg and Al-4%Zn-2%Mg alloy welds.Grain-structures grew slightly with the increase of heat input per unit length, though columnar grains were likely to be formed on the side of low heat input and granular grains were on the side of high heat input.In Al-4.5%Mg and Al-4%Zn-2%Mg alloy welds, feathery grains were observed.In 99.5%Al, Al-4.5%Mg and Al-4%Zn-2%Mg alloy welds, there were observed layer lines or solute bands which corresponded to grain-refined region as well as to alternate region of fine and coarse dendrite cells.If three dimensional heat flow during solidification was approximately ensured, the dendrite cell size increased parabolically with the heat input per unit length as predicted from the theory of dendritic solidification involving mass-transfer and heat flow theories. However, it increased linearly with the heat input per unit length, if three dimensional heat flow was not ensured because of full-penetration.Concentrations of solutes such as magnesium, zinc, iron and silicon in the dendrite cell matrix were likely to be decreased with the increase of heat input, while those of solutes in the dendrite cell boundary to be increased.