Microstructure and Hardness Analysis of Aluminum Alloy Gradient Plate Prepared by Friction Stirring After Heat Treatment

A friction stir joining technology was used in preparing a performance gradient aluminum alloy sheet through friction stirring. The sheet was treated by solution aging, and the metallographic structure and hardness of the sheet before and after heat treatment were analyzed. Results showed that the sheet with good hardness gradient distribution can be obtained by selecting appropriate process parameters. When the rotation speed of the stirring tool is 300 rpm, the feed speed of the stirring tool is 250 mm/min, the downward pressure of the stirring tool is 6.6 mm, the hardness distribution of the upper and lower surfaces and sections of the specimens with or without heat treatment improves, and the best gradient hardness distribution of the sections is obtained. The grains in the stirred region of the prepared gradient sheet obtained by each parameter are refined to a certain extent, especially after heat treatment. Grain changes are obvious, but the grains grow after heat treatment. The second phase precipitated after heat treatment is evenly distributed, and this is effect improves the hardness of the sheet. The aluminum alloy gradient material prepared in this paper can meet the requirements of the automobile industry and other molding plate performance requirements. It is also found that the friction stir joining technology can better prepare aluminum alloy gradient material, and the fabricated material has fewer defects than the continuous casting technology.