Effect Of Heat Treatment On Microstructure And Properties Of AZ80 Magnesium Alloy Cabin

Lightweight,high-strength and high-toughness components are an urgent need for aerospace,defense,military and other industries to reduce structural weight and improve operational technical indicators.Among them,the cabins are an important part of the rocket structure and the main load-bearing components.The realization of lightweight,integrated and precise manufacturing of cabins is an important requirement for the development of a new generation of aerospace equipment.In this paper,a commercial AZ80 magnesium alloy was used as the experimental material,and a new process of annular channel angular extrusion?ACAE?was used to prepare the cabin.And the effects of deformation and heat treatments on microstructural evolution and mechanical properties of the cabins were studied.This article focuses on the?-Mg₁₇Al₁₂2 dissolution behavior of the cabin after homogenization treatment,solution treatment?T4?,aging treatment?T5?,solution treatment and aging treatment?T6?,respectively.At the same time,the relationship between?phase microscopic characteristics and mechanical properties was revealed,which provides theoretical support for the manufacture of high-performance magnesium alloy cabins.The main conclusions can be drawn:?1?The as-cast alloy is mainly composed of?-Mg matrix,?-Mg₁₇Al₁₂ eutectic phase and insoluble Al-Mn phase,which is an uneven segregation structure.During homogenization treatment,temperature is the main factor affecting dendritic eutectic phase dissolve into the matrix.The higher the homogenization temperature,the more the dendritic eutectic phase is dissolved into the matrix,while the alloy is prone to over-burning.After the as-cast alloy was homogenized at 415?+16 h,the phenomenon of dendrite segregation was eliminated,and the elongation increased from 0.98%to 10.7%.?2?Deformation temperature strongly affected the microstructure and mechanical properties of extrusion.As the deformation temperature increases,the degree of microstructure unevenness decreases,and the grain size and texture intensity increase.The shear texture gradually disappears,and then transforms into a texture with a{0001}basal plane 20°deflections from the extrusion direction.The uneven microstructure and the coarse grains are not conducive to improving the mechanical properties of the alloy.The best comprehensive mechanical properties were obtained by ACAE process at 350?.Analysis of fracture showed that the vicinity of the intergranular phase in the extruded alloy is the main area for crack generation and propagation.?3?The T4 treatment causes the static recrystallization of the extruded alloy,which further led to increasement of the grain size,and the?phase dissolve into the matrix to form a uniform supersaturated solid solution.After T4 treatment,the strength of the alloy was reduced,while the elongation was greatly improved,and the fracture mechanism was changed to twin-induced fracture.The best solution treatment parameters of the extruded alloy at300?,350?,380?are 415?+2 h,415?+2 h,415?+1.5 h.?4?The precipitate characteristics of?-Mg₁₇Al₁₂2 are mainly controlled by the aging temperature.The results showed that the low temperature was beneficial to the precipitation of cellular structure and oval-shaped precipitate,and the high temperature was favorable to the precipitation of Widmanstatten structure,lath-shaped precipitate and intergranular precipitate.When the aging temperature increases,the volume fraction of the cellular structure decreases and the corresponding lamellar spacing increases,the Widmanstatten structure and intergranular precipitate are significantly coarsened;this leads to the weakening of the age-hardening effect of the alloy.?5?T5 treatment can not change the uneven structure formed by extrusion,?phase preferentially precipitates near the intergranular precipitate where Al atoms are enriched.In the T5 tensile specimens,cracks were likely to initiate near the brittle intergranular phase,resulting in a poor elongation.After T6 treatment,a large amount of?phase were uniformly precipitated from the supersaturated solid solution,the comprehensive properties of the alloy was significantly improved,and cracks tended to nucleate and expand in the precipitate free zone?PFZ?between the?-Mg matrix and the precipitated phase.?6?By comparing the microstructure and performance of the cabins after heat treatment,the optimal forming of ACAE and heat treatment process parameters of AZ80 magnesium alloy were determined:homogenization treatment?415?+16 h?+extrusion deformation?350?+0.5mm/s?+solution treatment?415?+2 h?+aging treatment?175?+30 h?.