Effect Of Solution Treatment On Microstructure And Properties Of 7050 Aluminum Alloy

In aerospace and military industries,Al-Zn-Mg-Cu alloy is widely used because of its high strength,low density and good molding process.However,with the rapid development of aerospace and military industry,the comprehensive performance of related products requires higher and higher requirements,not only for high strength but also for good corrosion resistance.Therefore,the study of Al-Zn-Mg-Cu alloys with high strength and good corrosion resistance has been the focus of aluminum alloy research.In this paper,7050 aluminum alloy,a typical representative of Al-Zn-Mg-Cu series ultra-high strength aluminum alloy,was studied by room temperature tensile test,intergranular corrosion test and electrochemical test,and the microscopic characterization techniques OM,SEM,EBSD and TEM were used to study the effect of solid solution treatment on the microstructure of 7050 aluminum alloy extruded material and 7050 aluminum alloy rolled material in the T6 state in a more systematic way.The effects of solid solution treatment on the microstructure(recrystallization degree,grain boundary type,second phase distribution)and properties(mechanical properties and resistance to intergranular corrosion)of 7050 aluminum alloy extruded materials and 7050 aluminum alloy rolled materials in the T6 state were studied more systematically.The main conclusions of the study.(1)Solid solution experiments were conducted to study the effects of solid solution treatment on the microstructure of 7050 aluminum alloy extruded and rolled materials by means of microscopic characterization,and the laws of the effects of solid solution treatment on the grain morphology,grain size,grain boundary type and second phase distribution of 7050 aluminum alloy extruded and 7050 rolled materials were analyzed.The grains of extruded and rolled 7050 aluminum alloy are mainly distributed in strips along the deformation direction,and fiber organization is formed when the deformation is large.After solid solution + T6 aging treatment,the grain orientation of 7050 aluminum alloy extruded material did not change much,and the grains were mainly transformed into substructure;the grain orientation of 7050 aluminum alloy rolled material changed significantly,and most of the grains underwent recrystallization transformation with the increase of solid solution time and solid solution temperature.After the solid solution regime of 490 ?/1 h + T6 aging,the 7050 aluminum alloy rolled material underwent complete recrystallization,and the grain distribution state tended to be close to the random state.(2)The effect law and mechanism of solid solution treatment on mechanical properties of 7050 aluminum alloy were investigated by room temperature tensile test and hardness test.7050 aluminum alloy extruded material and rolled material had poor strength,hardness and toughness.After solid solution + T6 aging,the strength,hardness and toughness of 7050 aluminum alloy were improved.Under the same heat treatment conditions,the 7050 aluminum alloy extruded material has higher strength and hardness compared with the 7050 aluminum alloy rolled material.Under the combined effect of precipitation strengthening and recrystallization softening,the 7050 aluminum alloy extruded material obtained a maximum strength of 674 MPa after solid solution + T6 aging treatment at 470 ?/30 min.(3)The effect law of solid solution treatment on the corrosion resistance of 7050 aluminum alloy material was analyzed by intergranular corrosion experiments and electrochemical experiments.The mechanism of corrosion crack formation and expansion of 7050 aluminum alloy was investigated by observing the microscopic changes of grains.In the corrosive environment,the corrosion cracks of 7050 aluminum alloy material are mainly generated at the location of large dislocation density and grain boundaries.Compared with the small-angle grain boundaries,the second phase formed at the large-angle grain boundaries is intermittently distributed,and the cracks are more likely to expand along the large-angle grain boundaries.