Study On Extrusion Process And Heat Treatment Of The New Al-Mg-Si-Cu-Zr Alloy

This paper investigated the extrusion process and heat treatment of a new Al-Mg-Si-Cu-Zr alloy, including the homogenization, the solution treatment and the aging treatment The differences of microstructures and mechanical properties of the extruded products afler different heat treatments are investigated and the effect of Zirconium on microstructures and mechanical properties of Al-Mg-Si-Cu-Zr alloy is obtained by testing the mechanical properties and analyzing the microstructure, so as to find an excellent technical parameters of extrusion and heat treatment.The grains of new Al-Mg-Si-Cu-Zr alloy ingot can be refined in DC casting by applying the low frequency electromagnetic field. When the alloy was homogenized at530℃for24hours, the interdendritic segregation and non-equilibrium phases almost dissolves completely and the microstructures are more uniform. The conductivity of the alloy can be improved from30.0%IACS in cast condition to41.8%IACS.The strength of the alloy extruded is increased greatly with raising solution temperature, but increase in solid solution time has a little effect. The time to reach peak-aging decreases with increasing in aging temperature, and the alloy owns a good ability of the overaging resistance when the aging temperature is slightly lower. T6treatment of the alloy is solution treat at555℃for2hours and ageing at170℃for24hours.The bar has it highest strongth in T6condition when extrusion temperature is480℃, while it will be low if the extrusion temperature reaches400℃. The T6properties of the extruded bar are438MPa in UTS,362MPa in yield strength,15.3%in elongation and41.6%IACS conductivity at extrusion ratio(λ)70, which is a good combination of deformation and heat treatment.Recovery and recrystallization are easy to take place in6xxx alloy, including the dynamic recovery and dynamic recrystallization occurring during the extrusion and the static recovery and recrystallization process. Zirconium added in the Al-Mg-Si-Cu-Zr alloy has an obvious influence on the microstructures and mechanical properties of the alloy after the extrusion and heat treatment. In the homogenization and aging process, lots of small Al3Zr phases precipited, which can inhibit recrystallization, refining grains and keeping fibrous micro structure after extrusion. In additon, Zirconium can make a certain contribution to the strength of the Al-Mg-Si-Cu-Zr alloy by refining grains, dispersion particles.