Influence of RE and Ni on the Microstructure and Properties of Al-Zn-Mg-Cu Aluminum Alloys

Influence of RE and Ni on the Microstructure and Properties of Al-Zn-Mg-Cu Aluminum Alloys
　　Aluminum and its alloys are being used more and more widely in not only military industry such as aerospace、ship-building, but also civil kinds such as construction、electricity、telecommunication, for its many wonderful particularities such as big mining reserves、low specific gravity、high specific strength、good conductivity, etc. During the last century, with the need of the rough competition of aerospace、ship-building, the great development of automobile、construction and so on, the improvement on handling them and its own advantages, aluminum has been the most widely used non-ferrous metal material.7xxx series Al-Zn-Mg-Cu alloys, known as ultra strength aluminum alloys,Block neodymium magnet  are widely used as structural parts on airplanes、space shuttles, and so on, for some of their valuable properties such as high specific strength and stiffness、good processing ability、corrosion resistance and split tenacity.
　　7A04 alloy is a type of ultra strength aluminum alloy that has been successfully used since an early time, which has a very high strength、good strengthening effects after being heat treated、medium plasticity in state of annealed or newly quenched. Its shortcomings are mainly low structural stability、low low-frequency fatigue strength and stress corrosion cracking.In order to advancing ultra high strength aluminum alloy, this paper focused on modern ultra strength aluminum alloy development, referred to a 7A04 aluminum alloy, added RE and Ni as additional alloying elements, took available advantages of metallographic analysis、X- ray diffraction analysis、scanning electronic microscopy and mechanics properties test, researched the influences on Al-Zn-Mg-Cu aluminum . alloy after RE and Ni being added gradually, found an optimum RE and Ni content.The crystal grain and eutectic compounds in the crystal boundaries were found thick when RE addition is low, while the grains became finer、thick eutectic compounds were less and boundaries were cleaner when more RE being added.The research also proved the strength in casting of cast Al-Zn-Mg-Cu aluminum alloy Block neodymium magnet became higher when Ni content was higher within 0～1.0%(wt). while after being T5 heat treated, the alloy with a 0.25%(wt) Ni content had the highest strength and length enlargement. new phases AlNi and Al7Cu4Ni were found in such state, and big strip-like phase AlNi3 was found in grain boundaries when Ni content was up to about 1%(wt), which greatly weakened the named alloy.The highest strength 402Mpa was found with a 1.0%RE and 0.25%Ni content in T5, meanwhile the length enlargement was up to 3.3%, while in casting they were 178MPa and 0.3%.