Abstract
A wrought Al-11.3Si-0.6Mg alloy under hot extrusion (T1), solution treatment (T4), and solution treatment + artificial aging (T6) states were friction stir welded at welding speed of 100 mm/min and rotation rate of 800 rpm. The effect of prior heat-treatment on the microstructure and mechanical properties of the welds were investigated. The results show that the microstructures of the nugget zones have little dependence on the initial states of the base material. In the nugget zones, complete recrystallized structures with equaxied grains in the Al matrix were formed under all conditions. The Si particles in the nugget zones are almost unchanged compared with those of their base materials (BMs) in the three states. In contrast, the joint efficiency of the obtained welds was very sensitive to the initial material condition. The joint efficiency under the T1 state is more than 90% due to the fact that the microstructure is almost unchanged, except for the slight coarsening of the Al matrix grains and some of the Mg2Si phases during the friction stir welding process. However, the joint efficiency in the T4 and T6 conditions is only 77.22% and 62.03%, respectively. The relatively low weld strength in the T4 and T6 conditions is due to the elimination of the solid solution strengthening and age hardening effects during friction stir welding. The hardness distributions along the cross section of joints are all W-shaped under T1, T4, and T6 conditions.
Highlights
As a solid-state process, friction stir welding (FSW) has the advantages of great heat input, is free of filler metal and shielding gas, and avoids melting compared with the fusion welding processes and can produce high-quality joints in aluminum alloys [1,2,3,4]
Recent studies found that Si phase refinement and massive Al grains can be achieved in Al-Si alloys through conventional plastic deformation, which improves their plasticity, Materials 2020, 13, 861; doi:10.3390/ma13040861
An Al-Si-Mg alloy ingot was prepared with commercially pure aluminum (Baikuang, Baise, China) and silicon (SichuanLande, Chengdu, China) without chemical modification by direct-chill (DC) casting at a pouring temperature of 760 ◦ C and a cast velocity of 200 mm/min
Summary
As a solid-state process, friction stir welding (FSW) has the advantages of great heat input, is free of filler metal and shielding gas, and avoids melting compared with the fusion welding processes and can produce high-quality joints in aluminum alloys [1,2,3,4]. Many researches have shown that FSW can produce fine microstructure, has an absence of welding defects, has low residual stresses, and has better dimensional stability in aluminum alloy joints [1,3,4]. Al-Si alloys are an attractive engineering material because of their high electrical conductivity, low coefficient of thermal expansion, and light weight [8]. Recent studies found that Si phase refinement and massive Al grains can be achieved in Al-Si alloys through conventional plastic deformation (rolling, extrusion, and forging, etc.), which improves their plasticity, Materials 2020, 13, 861; doi:10.3390/ma13040861 www.mdpi.com/journal/materials
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