| Ultra-high strength Aluminum Alloy material research has been the focus materials of aviation industry,with the rapid development of large aircraft,aluminum alloy has already became an important material in many key parts.However,the strength and hardenability limit its development.How to control the ratio of alloy elements is critical.In the paper,we designed and smelt nine kinds of 7000 series aluminum alloy,the factors of affecting the hardenability were studied and analyzed.Studied the effects of the main alloying elements Zn,Mg and trace element Mn on microstructure and properties of 7000 series rolled Aluminum Alloy.The microstructure and properties were investigated by XRD and EBSD analysis,Conductivity test,hardness tests,tensile,inter-granular and exfoliation corrosion resistance experiments.The main conclusions of the paper are as follows:(1)Through the study of eight kinds of 7000 series aluminum alloy on hardenability,found that flocculent precipitates with high Zr appeared away from quench side by SEM analysis,showed that the cause of hardenability decrease is Zr.Based on the analysis of the sum of the main alloy elements atomic radius difference,the trace elements Zr and Mn,the impurities of Fe and Si.Found that the smaller atomic radius difference,the better of hardenability is;Zr and Mn increased the hardenability,and Mn is greater than Zr;impurity elements Fe and Si will also decreased the hardenability.And when the main alloy elements of atomic radius difference and Si contents is smaller,which could maintain high hardenability with high Zr contents;when the content of Zr,Fe and Si is lower,it could maintain high hardenability with large atomic radius difference.(2)Effect of Mn on the microstructure and properties of 7000 series rolled aluminum alloy Al-9.94Zn-2.35Mg-2.53Cu-xMn-0.23 Zr was studied.The results showed that the addition of 0.41% of Mn and 0.25% of Zr can obviously inhibit the recrystallization and grain growth,and retain dislocations and low-angle grain boundaries after the solid solution and aging,have a certain effect of strengthening.The strength of the alloy with Mn in T6 is higher than the alloy without Mn,increased from 598.5 MPa to 617.6 MPa,but the strength decreased significantly after T76 aging,decreased from 617.6 MPa to 566.4 MPa and decreased by 8.3%.The Mn element can reduce the over aging time,which is not conducive to the strength under T76 aging.The Mn could reduce the exfoliation corrosion resistance and improve the intergranular corrosion resistance.(3)Effect of Mg and Mn on the microstructure and properties of ultra-high strength rolling aluminum alloy Al-9.1Zn-xMg-2.72Cu-xMn-0.26 Zr were studied.The results showed that Mg promote recrystallization.The increase of Mg leads to recrystallization and grain growth,but the recrystallization process consumes more dislocations and low angle grain boundaries,the strength of the alloy in the T6 aging has decreased.Compound addition of 0.41 Mn + 0.25 Zr can inhibit recrystallization and grain growth.Compound addition of 0.2 Mn + 0.25 Zr can not inhibit recrystallization,but can inhibit grain growth.The increase of Mg elements could reduce the intergranular corrosion resistance and improve the exfoliation corrosion resistance.In this experiment,the ultra-high strength aluminum alloy were developed,the composition is Al-8.94Zn-2.55Mg-2.63Cu-0.26 Zr.The tension strength reached 628.9MPa in T76 aging,and the elongation was 7.3%,the exfoliation corrosion grade reached the PB grade.(4)Effect of Zn element on microstructure and properties of ultra-high strength rolling aluminum alloy Al-xZn-2.62Mg-1.29Cu-2.0Zr was studied.The results showed that Zn promote recrystallization,and Zr inhibit recrystallization.When the Zn/Mg value exceeds 3.61,the increase of Zn can’t increase the aging precipitate strengthening phase,and the strength of the alloy decreased.The intergranular corrosion resistance will decrease with the crease of Zn,but it has little effect on exfoliation corrosion resistance.In this experiment,the ultra-high strength aluminum alloy was developed,the composition is Al-9.79Zn-2.71Mg-1.27Cu-0.15 Zr,the tensile strength has reached 682.2 MPa and the elongation is 6.2% under T6 aging,the tensile strength has reached 630.1 MPa and the elongation is 7.76% under T76 aging.The intergranular corrosion resistance and the exfoliation corrosion resistance have reached three and PC level,single-ended hardenability has also reached 80 mm,the comprehensive performances of the alloys are excellent. |
PDF Full Text Request