Effect On Microstructure And Properties Of The Al-Zn-Mg-Cu Alloy With Rare Earth La And Ce

Adding rare earth elements to the alloy is an important alloying and modification scheme.In order to meet the needs of new high-end aluminum alloy materials in aerospace,marine ships,aluminum wires,medical equipment,special equipment and other fields,the paper expects to develop a new high-strength and corrosion-resistant aluminum alloy material by adding rare earth elements to Al-Zn-Mg-Cu aluminum alloy.Based on the literature research,comprehensive cost and process factors,the alloying scheme with trace La and Ce was adopted.In this study,the Al-Zn-Mg-Cu alloy was melted by well heating furnace.The influence of La,Ce and addition of rare earth elements on the microstructure,phase composition and properties of Al-Zn-Mg-Cu alloy was studied by means of chemical composition analysis,differential thermal analysis,metallographic microscope,scanning electron microscopy,transmission electron microscope and microhardness tester,normal temperature mechanical tensile test.The analysis of chemical composition shows that the addition of rare earth elements La and Ce can improve the element segregation under the same smelting and casting conditions.The microstructure and energy spectrum analysis show that the morphology and structure of the Al-Zn-Mg-Cu alloy change with the addition of La and Ce.The second phase mainly consists of?(Mg Zn₂)phase,?(Al₂Cu Mg)phase and alznmgcu phase rich in La and Ce.Further analysis shows that when the content of La and Ce is 0.3%(the content in the following articles are all mass fraction(wt.%)),the coarse massive phase can be seen in the microstructure,which reduces the strength and toughness of the alloy;when the content of La and Ce is 0.05%,the phase in the alloy is fine,which can effectively play the role of micro alloying It can improve the strength of the alloy.After homogenization treatment at 400?/10h+470?/40H+480?/30h,the intragranular segregation and unbalanced crystalline phase produced in the casting process are basically eliminated,and the soluble phase elements are dissolved in the matrix,such as the second phase particles?(Mg Zn₂),?(Al₂Cu Mg)and Al₂Cu.After heating and rolling,a large amount of?(Mg Zn₂)phase is formed again,and the grains are deformed and elongated along the rolling direction.After solution treatment and artificial aging treatment,fine and dispersed strengthening phase particles,mainly Mg Zn₂ phase,are precipitated in the rolled sheet,and the microstructure and properties of the alloy are further improved.The solution system is 470?/35min+480?/25min.After single-stage and double-stage artificial aging treatment and adding 0.05%rare-earth element Ce,the micro hardness value is195.4HV,the tensile strength is 588MPa,the yield strength is 525MPa and the elongation is14.9%,the conductivity is 19.14ms/m,and the exfoliation corrosion resistance is better than that with 0.05%La,which can reach EA level.