Application of electron beam welding technique for joining coarse-grained and ultrafine-grained plates from Al-Mg-Si alloy

Abstract

In the present work, the attempt to weld coarse (CG) and ultrafine-grained (UFG) Al-Mg-Si alloy using an electron beam welding technique has been taken. Welding parameters were selected in a way to reduce the energy input, and thus the heat-affected zone (HAZ) and the evaporation of elements with high saturated vapor pressure. The UFG microstructure was beneficial in obtaining smaller grains in the fusion zone (FZ) and HAZ, resulting in higher mechanical strength than weldments from CG Al-Mg-Si alloy. The weld efficiency for CG alloy was 80 %, while for the UFG sample - 68 % (82 %, compared to CG base material). The reasons for a drop in mechanical properties in the FZ were a dissolution of strengthening precipitates and an increase in grain size. Also, the evaporation of Mg (alloying element) and Zn (impurity) occurred to a larger extent. The rupture in both welds occurred in the columnar dendritic area in the FZ, characterized by the elongated dendrites and cube texture that favoured the rupture.