| The 6xxx and 7xxx aluminium alloys are two typical heat treated and strengthened aluminium alloys that are widely used because of the high mechanical properties that can be obtained after solution ageing.Solid solution and ageing treatments allow the formation of different second phases from the elements in the matrix without the addition of alloying elements at a certain temperature and for a certain period of time,using these second phases of different shapes and sizes to impede the movement of dislocations and thus improve the mechanical properties of the alloy.In this paper,6061 and Al-9.2Zn-2.4Mg-1.5Cu alloys were subjected to ageing treatment in a chamber furnace and hydrothermal environment after solid solution treatment to explore the effects of different ageing temperatures and times on the mechanical properties and microstructure of the alloys.The effects of aging on the mechanical properties and microstructure of Al-9.2Zn-2.4Mg-1.5Cu aluminium alloy after solid solution treatment were investigated in a hydrothermal environment.The effect of aging time and aging temperature on the mechanical properties of the aluminium alloy was investigated,the ideal heat treatment process parameters were obtained,and the feasibility of aging treatment in a hydrothermal environment was explored.The main conclusions were obtained as follows:(1)After solid solution,6061 alloy grain recrystallization,and recrystallization grain size with the increase of solid solution temperature and increase,the best solid solution temperature of 6061 alloy is 540 ℃,when the alloy tensile strength of218 MPa,elongation 31%.(2)Under the aging environment of the chamber furnace,the best aging regime is 170°C/12 h at a solid solution temperature of 520°C,with a tensile strength of324 MPa and an elongation of 16.7%.The best ageing system is 190°C/12 h at a solid solution temperature of 530°C.The alloy has a tensile strength of 337 MPa and an elongation of 14.3%.The optimum ageing regime is 170°C/8h at a solid solution temperature of 540°C.The alloy has a tensile strength of 334 MPa and an elongation of 16.3%.Considering the economy and energy consumption,the best heat treatment system for the box furnace aging environment is 540°C/1h solid solution water quenching + 170°C/8h.(3)Under hydrothermal ageing environment,the best ageing regime is 170°C/8h at a solid solution temperature of 520°C.The alloy has a tensile strength of 292 MPa and an elongation of 15.7%.The best ageing regime at 530°C is 180°C/8h,with a tensile strength of 300 MPa and elongation of 14.7%.The optimum ageing regime is180°C/12 h at a solid solution temperature of 540°C.The alloy has a tensile strength of334 MPa and an elongation of 16.7%.Based on the optimal performance factors,the optimum heat treatment regime for a hydrothermal ageing environment is 540°C/1h solid solution + 180°C/12 h ageing.(4)Al-9.2Zn-2.4Mg-1.5Cu alloy due to the Zr element and the extrusion effect,the plate is still fibrous after solid solution,but there is a large number of subcrystalline structure within the crystal,and with the increase of solid solution temperature,the number of subcrystals increases.(5)In the hydrothermal environment,the optimum ageing regime is 120°C/20 h at a solid solution temperature of 465°C.The tensile strength of the plate at this time is 659 MPa,corresponding to a yield strength of 601 MPa and an elongation of 7.3%.The optimum ageing regime is 120°C/10 h at a solid solution temperature of 475°C.The plate tensile strength is 733 MPa,yield strength 694 MPa and elongation 13%.On balance,the optimum heat treatment regime for Al-9.2Zn-2.4Mg-1.5Cu in a hydrothermal environment is 475°C/1.5h solution + 120°C/10 h ageing. |
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