Assessment of cold deformation effects on yield-to-tensile ratio and dimensional stability of an aluminium alloy extruded tube

This study was carried out to assess the effects of cold deformation on the dimensional stability and yield to tensile ratio in AA6061-T6X aluminium alloy. Dimensional changes observed after the machining are mostly related to metal forming operations such as extrusion or forging and solution heat treatment processes. These processes generate severe stresses inside the material which causes machining distortions and the final component fails to meet dimensional tolerance limits. Investigations were made on as-extruded pipe of AA6061 aluminium alloy having outer diameter ~135 mm and wall thickness of 30 mm. The specimens were cold deformed via sinking and or stretching process in different combinations before and after the solution heat treatment. Finally, the pipes were artificially aged at 160 °C to get T6X tempers. All the specimens were tested for mechanical properties and machined to check the dimensional stability. The results showed that the degree of cold deformation after the solution heat treatment has substantial effects on dimensional stability and yield-to-tensile ratio of the alloy. Furthermore, it was observed that variation in the hardness values across the complete length of the pipe got minimized when the cold working was done in two steps, before and after the solution heat treatment.