7249 Aluminum For Corrosion Resistance And Mechanical Effects Of Rare Earth

7249aluminum alloy is a kind of structure material known for aircraft main landing gear. However, the strength and the corrosion resistance do not meet the requirements at the same time. To facilitate the solution to this problem, the effects of added RE alloying elements, heat treatments on the mechanical properties and microstructures of7249aluminum alloy were investigated with various experimental and testing methods, such as optical microscopy, scanning electron microscopy, TG-DTA thermal analysis, hardness testing, conductivity testing and properties testing. The major conclusions were drawn as follows:(1) There is low-melting product which began to melt at479℃in common ingot of7249aluminum alloy. The product could dissolve entirely into the matrix of the alloy at450℃for24hours.(2) The intensity of7249aluminum alloy increases gradually after first order ageing treatment whether it is in the air,30%of PAG quenching medium, water quenching. After three-step aging, the intensity increases at first then decrease. The tensile strength is586.23MPa, yield strength is526.72MPa, elongation is13.8%, conductivity is33.1%IACS of RRA treated alloy by quenching at30%PAG quenching medium shows the best performance.(3) The main intergranular corrosion product is Al2O3of7249aluminum alloy. Intergranular corrosion of alloy by three-step aging treatment is more serious than first order aging treatment whether it is in the air,30%of PAG quenching medium or water quenching.(4) The alloy without RE addition which hardness is177.04, conductivity is33.16%IACS. The hardness is194.5and conductivity is36.43%IACS by adding0.07%rare earth, those are maximum values. The hardness is184.45and conductivity is33.1%IACS by adding0.03%RE. Intergranular corrosion of7249aluminum alloy by adding0.03%RE shows the best performance, average depth is22.06μm and maximum depth is32.22μm, and which exfoliation corrosion grade is EA. The results show that7249aluminum alloy with0.03%RE addition has an excellent corrosion resistance properties. Considered comprehensive performance, the alloy with0.03%RE has an optimal performance.