Thermo-mechanical processing of Al–Mg–Si(Cu) alloy extrusions based on dynamic stretching

Abstract In the first part of the work, the 3-step homogenization procedure was carried out for AlMgSi(Cu) alloy, aimed at obtaining billets microstructure with numerous fine particles of strengthening phases and increased solidus temperature. In the second part of the work, an original on a global scale prototype device for the dynamic stretching of extruded profiles before artificial ageing, was proposed and tested in semi-industrial conditions. The thermo-mechanical treatment of extruded hollow profiles from AlMgSi(Cu) alloy with 1.22% content of copper was performed with dynamic deformation range: 0.25%, 0.5%, 1%, 1.5% and 2%. The microstructural inspection was performed in the welding area and outside the weld for variant after only extrusion and for variant after extrusion and dynamic stretching before artificial ageing. It was revealed that the designed three-stage homogenization treatment led to dissolution of soluble phases present in the as-cast billets microstructure, which caused significant increase in solidus temperature, from 509 °C in as-cast state to 573 °C after completed soaking. The application of dynamic deformation during the straightening of aluminium profiles after hot extrusion with water cooling on the press run, led to the induced favourable changes in the microstructure of the alloy, which translated into a significant increase in UTS of about 11%.