Composite Add Zr, Cr And Pr On The Al-zn-mg-cu Alloy

Intensive precipitates decrease fracture toughness and resistance to stress corrosion cracking because of its continuous distribution along the grain boundary, which limit its potential for application, while it increse the strength of Al-Zn-Mg-Cu alloys. The contradiction among high strength, high toughness and remarkable corrossion resistance of aluminium products are not well solved so far. A effective method is demand for controlling the boundary structure of alloys, and minor alloying is one of it.By developing a new dispersoid to control boundary structure of Al-Zn-Mg-Cu alloys was studied in this paper. The formation and high-temperature stability of (Zr, Pr)Cr2Al20 dispersoids were investigated by optical microscopy, X-ray diffraction, transmission electron microscope and scanning electron microscope with energy dispersive spectrdmeter. Effect of the dispersoids on recrystallization of Al and on mechanical properties and corrosion resistance of Al-Zn-Mg-Cu alloys were studied.Multi-component (Zr, Pr)Cr2Al20 dispersoids with CeCr2Al20 structure were formed by combined addition Zr, Cr and Pr in Al. Its high-temperature stability and hardening effects on Al are signignificantly better than PrCr2Al20 dispersoids. Its ability on inhibiting recrystallization of Al are remarkable compared with Al3Zr and PrCr2Al20 dispersoids, and the effects reinforced as the amount of the dispersoids increased.With the similar effects in Al, (Zr, Pr)Cr2Al20 dispersoids can strongly retard recrystallization and growth of sub-grain of Al-Zn-Mg-Cu alloys. This lead to increase of the strength, elongation, fraction toughness and resistance to intergranular corrosion, exfoliation corrosion and stress corrsion cracking of alloys. Furthermore, the more (Zr, Pr)Cr2Al20 dispersoids formed in alloys the more remarkable ability of inhibition on recrystallization were showed. Therefore, the mechanical properties and corrosion resistance of alloys were improved evidently by increasing the dispersoids. The value of KIC and KISCC of designed alloy Al-3.79Zn-2.97Mg-1Cu-0.1Cr-0.05Pr-0.05Zr were reached to 33.2 and 27.4 respectively and itsσb andδwere 732MPa and 10.8%.