Heterogeneity of microstructure and mechanical properties of friction stir welded joints of Al-Zn-Mg alloy AA7039

摘要

Al-Zn-Mg aluminium alloy AA7039 was friction stir welded in order to investigate the influence of structural heterogeneity on mechanical properties of welded joints. Quality and mechanical properties of the developed weld joints were assessed by conducting bend, tensile and microhardness tests. Optical and scanning electron microscopy was used to analyze the microstructure and fracture surfaces respectively. It was found that joints were heterogeneous as different layers of joint exhibited significant heterogeneity in respect of microstructure and mechanical properties. Weld nugget grain size was found to decrease from top to bottom. Top layer of joint was strongest while middle layer was weakest. Weight % of Zn and Mg decreased from top to bottom layer of the joint. Mode of fracture was also found to be different for different layers of joint.