Effect Of Ultrasonic Casting On The Microstructure,Mechanical And Corrosion Resistance Properties Of7085Aluminum Alloy

Abstract:The tensile test, hardness examination, corrosion resistance test, polarization curve test, electrical conductivity and microstructure (OM), scanning (SEM), transmission electron microscopy (TEM) characterization and analysis method, calculation software Thermo-Calc, JmatPro based on the thermodynamic, first principles method based on density functional theory were applied in the article, some research works around Al-7.8Zn-1.6Mg-1.8Cu-0.12Zr alloy have been done as follows: the phases may present in the alloy were calculated,and it’s content, heat of formation, cohesive energy, fermi energy and elastic constant for the phases were calculated, according to the calculation result the corrosion resistance, strength and toughness may caused by the phases were studied; effect of Ultrasonic casting on Microstructure uniformity of alloy,effect of ultrasonic casting on mechanical and corrosion resistance properties of the alloy.The conclusions are listed as follows:(1) The equilibrium phases mainly include MgZn2, Al2Cu and Al3Zr in the alloy, it’s formation was found to an exothermic process. And among them, MgZn2has the largest electrode potential difference with a-Al, they are prone to form micro batterys, thus decrease the corrosion resistance of the alloy, while the electrode potential difference between Al2Cu and α-Al is not much. Al3Zr has the biggest bulk moduli, shear moduli, elastic moduli, and young’s moduli, it increases the alloy’s strength and toughness most.(2) Ultrasonic casting did a good job in the grain refinement and uniform the composition for Al-Zn-Mg-Cu alloy. Under homogenizing treatment of473℃/24h,the grain boundary of the ingot were clear and straight. Ultrasonic casting help elements diffusion and solid solution in the ingot, the genetic effect of as cast alloy ingot after homogenization and hot deformation process the normal casting alloy got maximum hardness under470℃/120min treatment, ultrasonic casting alloy got maximum hardness under470℃/90min treatment. Ultrasonic casting can aggravate the diffusion of alooy elements, which leads the Al3Zr particles work more efficient on inhibition of recrystallization and grain refinement in the alloy.(3) The result show that compared with T6aging treatment the alloy under T73aging treatment got excellent resistance ability for corrosion at the expense of strength,under the condition of RRA aging treatment the alloy got excellent resistance ability for corrosion and still keep the strength as strong as under T6aging treatment for the Al-7.8Zn-1.6Mg-1.8Cu-0.12Zr aluminum alloy casting with ultrasonic introduced. Compare with the alloy without melt ultrasonic treatment, the precipitates are uniform distributed and the part of precipitates coarsened, the uniform distribution of tiny precipitates have a positive impact on the strength of the alloy, the coarsened precipitates did a negative effect on the strength, but it can improve the corrosion resistance of the alloys,due to the cavitation,acoustic streaming and vibration effects brought by ultrasonic,which increased the solid solubility of alloying elements in the ingot and vacancy desity of the matrix,under the same aging treatment.