| In this paper, ZM5-xRE magnesium alloy were prepared by adding Al-RE master alloys to ZM5 magnesium alloy. The influence of mixed rare earth elements and heat treatment on the microstructure and corrosion resistance was investigated by optical microscope, scanning electron microscope (SEM), energy spectrum analysis (EDS) and X-ray diffract analyzer (XRD).Microstructure studies have shown that the formed Al3Ce phase and Al11La3 phase distributed at the grain boundary in form of granular and rod. The cast organization of ZM5 can be refined by adding 0.1% mixed rare earth,the discrete and coarse bone-likeβphase into a continuous network. But the continuous network structure starts to crumble when continuing to add the mixed rare earth. After solution treatment,β-phase dissolved intoαphase, the grain geometry size ofαphase increases, the composition becomes uniform. After aging treatment, theβ-phase distributed in the grain boundary as granular and sheet.Corrosion tests shows that the corrosion resistance of casting state ZM5-xRE is the best, the corrosion resistance slightly decreased after solution treatment, the corrosion resistance after aging treatment is the worst; with the increase of mixed rare earth, the corrosion resistance of ZM5-0.1RE is best for the casting state and heat samples treatment.Based on the analysis of corrosion morphology, corrosion products and corrosion products film, this paper researched the influence of microstructure on the corrosion resistance and concluded the mechanism of the mixed rare earth and heat treatment can improve the corrosion resistance of magnesium alloy ZM5 as follows.①Adding appropriate amount of mixed rare earth refines the microstructure of alloy, increases t boundary area in unit area, increasing the spread resistance of corrosion. Between the samples of casting state and heat treatment, the corrosion resistance of ZM5-0.1RE is the best which owns the smallest grain size.②after adding 0.1% of mixed rare-earth , theβ-phase of cast ZM5 magnesium become into continuous network from the discrete and thick bones shaped, act the role of corrosion barriers, limit transfer of corrosion from oneαgrain to another .③The main component of corrosion product film of ZM5-xRE sample is Mg(OH)2 which texture is loose and easily damaged by Cl- and SO42-, can not protect the base effectively and stable. The formed Al3Ce and Al11La3 after adding mixed rare earth can enter the corrosion products film, improve the compactness of the corrosion product films.④The solution treatment can make the components uniform, reduce the potential difference of micro-region and also improve their corrosion resistance ofα-phase, but the grain size increase and the impediment of grain boundary declined, so the corrosion rate slightly faster than the casting state.⑤After aging treatment, the distribution of precipitatedβphase is granular and needle, which can not act as corrosion barrier, mainly act as cathode in corrosion galvanic and accelerate the corrosion. And larger the grain size, the impediment role of grain boundary is much poor, so the corrosion resistance of the sample is the worst.
|
PDF Full Text Request