Effect Of Alloying And Retrogression And Re-aging Treatment On Microstructure And Properties Of7075Aluminum Alloy

In this paper,7075aluminum alloys containing Ti (mass fraction0.00%、0.04%、0.08%、0.12%、0.17%、0.22%) were prepared by ingot metallurgy method toinvestgate the effect of Ti content of the property of7075aluminum alloy. The alloyswith Ti content of0.17%and Er content of0.30%were also prepared to study theeffect of Er on the property of7075aluminum alloy. The alloys with different ratio ofZn to Mg were also prepared to research the properties of the7075aluminum alloy.Furthermore, the effect of retrogression and re-aging (RRA) treatment process on themicrostructure and mechanical properties of7075aluminum alloy were mainlystudied in this paper to optimize the heat treatment process. The changes ofmicrostructure under different process conditions were analyzed by opticalmicroscopy, scanning electron microscopy and spectroscopy. The results showed that:(1) With the content of Ti increased to0.17%, the grain sizes of7075alloy weregreatly refined. This resulted from the good refining agent of Al3Ti, with goodinterface coherency of Al. Under T6aging treatment the tensile strength and yieldstrength of the alloy were590MPa and545MPa respectively, with11.2%ofelongation. After the RRA treatment,the mechanical properties increaseddramatically. The tensile strength and yield strength of the alloy were623MPa and572MPa respectively, with13.2%of elongation. The sample fracture were typicalductile dimple fracture.(2) After being added with mass fraction0.30%Er, the Structure of7075alloywere greatly refined. Under T6aging treatment the tensile strength and yield strengthof the alloy were585MPa and528MPa respectively, with8.5%of elongation and724of the quality factor. Compared with the mechanical properties of Er-free alloy, theabove properties improved2.63%and2.33%respectively,but the quality factor andthe plasticity was low. The optimized retrogression and re-aging(RRA) treatmentprocess was120℃/16h+180℃/10min+120℃/16h.The tensile strength andyield strength of the0.30%Er7075ally were645MPa and603MPa respectively,with11%of elongation and801of the quality factor. After the RRA treatment,the mechanical properties increased dramatically. Compared with the T6states, the aboveproperties improved10.26%,14.20%and29.41%and10.64%respectively.(3) When the ratio of Zn to Mg was4.5, the tensile strength and yield strengthof the alloy under T6were650MPa and620MPa respectively, with2.8%ofelongation and717of the quality factor. The strength increased dramatically,but theplasticity was low. This low performance might be resulted from the grain boundarycoarsening of phase. The optimized retrogression and re-aging(RRA) treatmentprocess was465℃/2h+120℃/12h+190℃/5min+120℃/16h. The tensile strength andyield strength of the ally were727MPa and703MPa respectively, with8.3%ofelongation and865of the quality factor. The plastic of the alloy were improved andhad great significance to the production of life.(4) During the RRA treatment, the boundary thick discontinuous phase and thesmooth phase in large and small angle were formed. This would be beneficial to thestrength and toughness properties of the alloy.