An Investigation On Microstructure And Properties Of Al-Zr-Yb(Er)Alloys

Abstract:The pure aluminum, Al-0.2Yb, Al-0.2Zr, Al-0.2Zr-0.2Yb, Al-0.3Zr-0.2Yb, Al-0.2Er, Al-0.2Zr-0.2Er and Al-0.3Zr-0.2Er alloys were prepared using ingot metallurgy processing. The hardness, tensile strength and electricial conductivity of experimental alloys at different treatments (as-cast, aged, cold-rolled, annealed) were tested. And the microstructure of these alloys at various treatments were studied using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy(TEM), high resolution electron microscopy(HREM) and scanning transmission electron microscopy(STEM). The synergetic effect of Zr and RE (Yb and Er) on the alloys were discussed. The results are as follows:(1) The peak vicker microhardness of Al-0.2Zr-0.2Yb is480MPa duing isothermal aging at400℃, which is significantly higher than the summation of that in Al-0.2Yb and Al-0.2Zr alloys. The strengthened hardening of Al-0.2Zr-0.2Yb alloy is attributable to the precipitate of nano-sized, core-shell structured Al3(Yb,Zr) particles. The core of the precipitate is rich in Yb while the Zr mainly segregates in the shell of the precipitate using STEM;(2) The core-shell structured, strengthened hardening and remarkable coarsening resistance of Al3(Yb,Zr) particles are attributable to the synergetic effect of the Yb and Zr. The Yb which is higher diffusivity is firstly precipitated in the alloy, stimulates the decomposition of Al-Zr, while the sluggish Zr retards the coarsening rate of precipitates. The rare earth element Yb can change the morphology and distribution of Fe-phase. After soluting at620℃, the aged Al-0.2Zr-0.2Yb alloy precipitates coarse Al (Yb,Zr) particles.(3) The peak stress of cold-rolled Al-0.2Zr-0.2Yb alloy is180MPa,49MPa higher than that of pure aluminum. The cold-rolled Al-0.2Zr-0.2Yb and Al-0.3Zr-0.2Yb alloys possess remarkable heat resistance. The ending temperature of recrystallization for Al-0.2Zr-0.2Yb alloy is470℃while the temperature of Al-0.2Yb is360℃. The increase in recrystallization temperature is caused by the pinning effect of Al3(Yb,Zr) particles on dislocation, subgrain boundary and grain boundary.(4) Owing to the synergetic effects of Zr and Er, the peak vickers microhardness of Al-0.2Zr-0.2Er is440MPa duing isothermal aging at400℃, which is higher than the summation of that in Al-0.2Er and Al-0.2Zr alloys. Al-0.2Zr-0.2Er alloy precipitates diffuse and core-shell structured Al3(Er,Zr) phases. The Al3(Er,Zr) precipitates have remarkable coarsening resistance and the time exponent for the precipitates is smaller than that for Al3Er phases.(5) The peak stress of cold-rolled Al-0.3Zr-0.2Er alloy is178MPa, due to the synergetic effects of Zr and Er. The cold-rolled Al-0.2Zr-0.2Erå'ŒAl-0.3Zr-0.2Er alloys possess remarkable heat resistance. The Al-0.3Zr-0.2Er alloy has excellent recrystallization resistance and the ending temperature of recrystallization for Al-0.3Zr-0.2Er alloy is485℃.