China Aluminum Network reports that 7050 aluminum alloy is a high-strength aluminum material that can be heat-treated and strengthened. It is known for its good castability, formability, and overall performance. However, traditional arc welding methods often lead to defects such as porosity, cracks, and undercut, especially when dealing with ultra-high strength aluminum alloys like 7050. This poor weldability, combined with a higher susceptibility to hot cracking, has significantly limited the industrial application of 7050 aluminum alloys. In contrast, friction stir welding (FSW) offers an efficient, high-quality, eco-friendly, and cost-effective alternative for joining high-strength 7xxx series aluminum alloys. This study focuses on single-pass butt joint friction stir welding of 8mm thick 7050-T7451 aluminum alloy plates, analyzing both the microstructure and mechanical properties of the resulting joints. The test materials used were 8mm thick 7075-T7451 aluminum alloy plates, and the stirring tool was made from H13 hot die steel. The chemical etching solution consisted of 15ml HCl, 1ml HF, 2.5ml HNO3, and 95ml H2O. Microstructural analysis was conducted using an Optelics TMS130 microscope. Tensile testing was performed on a CSS-44100 electronic universal testing machine, while hardness measurements were taken with a HX-1000 microhardness tester. During the welding process, continuous dynamic recrystallization occurs in the weld nugget, leading to the formation of fine equiaxed grains. The heat-affected zone exhibits an arc-shaped structure due to the combined effects of mechanical force and thermal cycling, and the grain size in this area tends to coarsen. At a rotation speed of 375 rpm and a welding speed of 100 mm/min, the tensile strength of the joint reaches up to 88.6% of the base metal. The hardness distribution shows a "W"-shaped pattern, with lower values typically observed at the transition between the heat-affected zones on the retreating side. These findings highlight the potential of FSW in improving the quality and reliability of 7050 aluminum alloy joints in industrial applications.
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