Effect of Mg₂Si Phase on Extrusion of AA6005 Aluminum Alloy

Abstract

The extrusion behavior and mechanical properties of aluminum alloys are very sensitive to the microstructure of the billets after homogenization. In order to optimize the homogenization practice for the extrusion process, the influence of different cooling rates from soaking temperature during homogenization was investigated for an AA6005 alloy. The specimens were soaked at 580°C for 8 hours, and then cooled by 3 different cooling rates: water quenching, air cooling and furnace cooling. The homogenized microstructures from specimens exhibit an increase in both amount and size of Mg₂Si particles with a decreasing cooling rate. The hardness at room temperature and the flow stress at preheating temperature (450°C) and real extrusion temperatures (500–550°C) also generally decrease with a slower cooling rate. However, re-precipitation of Mg₂Si is observed upon reheating to 450°C and dissolution is observed at 500°C and 550°C. A fast cooled billet is identified to have fully solutionized microstructure but requires higher extrusion pressure and is sensitive to preheating rate, while a slow cooled billet is easier to extrude but is not sufficiently solutionized after extrusion.