It is well known that medium strength aluminum alloys such as 6005, 6061 and 6063 have been widely used in structural units for their good combination of strength, resistance to corrosion and hot extrudability etc. However, there are some limitations of heat treatment in their big-long extrudates.
In this present study, the effects of Mn addition and homogenization heat treatment on tensile properties in as-extruded Al-Mg-Si-(Mn) alloys have been studied to develope the new Mn bearing alloy without heat treatment after shaping process. The chemical compositions of the aluminum alloys used in this study are 0.6wt.%Mg, 0.7wt.%Si (1.0wt.%$Mg_2Si$) and 0.5wt.%Cu. The ingots fabricated in air induction furnace were hot extruded at the range of 400℃~500℃ with constant extrusion ratio(9:1) and speed(10mm/sec) to determine the optimum extrusion conditions. When the extrusion process is conducted at 450℃, extrusion press effect is the largest. Three kinds of homogenization heat treatment were conducted to determine the optimum condition before extrusion process. Adding manganese to Al-Mg-Si based alloy in the range of 0.2wt.%~1.0wt.%, Mn-dispersoid which is composed of Al, Mn and Si is formed. After extrusion process, the size and density of Mn-dispersoid are somewhat reduced. But 560℃, 10hrs homogenization condition is effective in view of Mn-dispersoid distribution and size. As a result, this condition gives a best tensile properties. Also, as the content of Mn is increased, the amount of Mn-dispersoid is increased without changing the morphology and its size. Although the effect of Mn addition is small in peak aged condition of 1.0wt.%Mn bearing alloy(1.0Mn alloy) designed for this study, its tensile properties are better than those of commercial 6061 and 6005 which amount of Mn+Cr is limited to below 0.5wt.%. So, Heat treatments are also available for small extrudate unit in 1.0wt.%Mn bearing alloy.
