Effects Of Zr And Electromagnetic Field On The Microstructure And Properties Of High Strength Aluminum Alloys

As the high strength and heat-resisting aluminum alloy of Al-Cu-Mg series.2E12 aluminum alloy is the irreplaceable skin material of aerocraft.2E 12 aluminum alloy,exploited on the basis of 2A 12(2024) alloy by decreasing contents of Fe and Si,has high-purity and high performance.2E12+XZr billets were prepared by different continuous casting processes(direct continuous casting,soft-contact electromagnetic continuous casting and electromagnetic continuous casting) in this article.The billets were processed by compression stress formation (free forging or isothermal hot extrusion) and T4(solution temperature:495℃,solution time: 60min and nature age-hardening time:96h) or T6(solution temperature:495℃,solution time: 60min and artificial age-hardening time:10h) heat treatment in turn.The effects of Zr and electromagnetic field on the microstructure and mechanical properties of 2E12 aluminum alloy were studied by using optical microscope,hardness measurement,tensile test, scanning electron microscope and experimental of fatigue crack growth rate et al.As-cast microstructures of 2E12 alloy can be refined with an addition of Zr and characterized with equiaxed grains.Zr can remarkably improve the properties of alloys under T4 and T6 treatment.The strengthening mechanism is considered as fine grain strengthening, dispersion strengthening and deformation strengthening.Zr has little effect on the process of nature age-hardening of 2E12 alloy,but it could delay the appearance of peak-ageing time of artificial age-hardening and extends the peak-ageing time at 190℃.On the condition of R=0.1, the fatigue crack growth rate(da/dN) of 2E12+0.3Zr alloys is lower than that of 2E12 alloys. The addition of Zr could improve the fatigue durability of 2E 12 alloys.2E12+0.14Zr billets,prepared by soft-contact electromagnetic continuous casting,were processed by isothermal hot extrusion and T4 heat treatment in turn.Effects of solution times on the microstructure and mechanical properties of 2E12+0.14Zr alloys were studied.The results show that,the strength of the alloys increases with the solution time.The alloys have better combination property when the solution time is 60min,there into.the tensile strength and elongation percentage reach to 538MPa and 23.3%,respectively.As solution time lengthens to 90min,the plastic nature of alloys become fall down. The effects of electromagnetic continuous casting on the microstructure and mechanical properties of 2E12 aluminum alloy were studied.The results show that,the EMC alloys have better microstructure and excellent surface because of the electromagnetic stirring and electromagnetic force during the EMC progress.The grain sizes of EMC alloys decreased from 58μm to 36μm.Mechanical properties of EMC alloys are improved with tensile strength. yield strength and elongation percentage increase by 9.0%,10.3%and 61.2%,respectively. After free forging and same heat treatment,tensile strength,yield strength and elongation percentage of EMC alloys under T4 treatment still raise about 4.0%,8.9%and 7.7%.The fatigue durability of EMC alloys under T4 treatment could improve,too.Mechanical properties of EMC alloys under T6 treatment are improved with tensile strength,yield strength increase by 10 MPa approximately.