| Magnesium alloys, due to their many distinct advantages over other structural materials, such as low density, high modulus, good machineability, excellent castability, superior damping characteristics and availability, have been considered as a most ideal metal structure materials for aeronautics and astronautics, automobile, electronic communications industry to realize lightweight,however, the poor corrosion resistance and mechanical properties of magnesium alloys has limited their further application. AM series alloys have been widely used in the industries, and how to improve their mechanical and corrosion resistance has been a key problem to be solved urgently. In the present work, the effect of Zn and heat treatment on microstructure and properties of AM60-2%RE alloy were studied by many analysis and testing means, such as optical microscope(OM), X-ray diffractometer(XRD), scanning electron microscope(SEM) with energy dispersive spectrometer(EDS), tensile testing, electrochemical polarization, electrochemical impedance spectroscopy measurement and so on.After the addition of minor Zn, the microstructures of as-cast AM60-2%RE+x%Zn alloys were all composed of ?-Mg matrix, Al4 RE, Al11RE3, a little Mg17Al12 and Al3 Mn, however the volume fraction of Al4 RE and Al11RE3 phases increased, which was distributed intermittently on the grain boundary. The addition of minor Zn was mainly solution into ?-Mg matrix, did not formed new phase with other elements. With the increase of Zn,the tensile strength and hardness of as-cast experimental alloys were significantly increased, while the impact toughness, elongation and thermal diffusivity decreased largely. At 0.8% Zn, the tensile strength and hardness increased to 185 MPa and 62 HV,which were increased by 10.3% and 8.7% in comparison with that of 0.2% Zn alloy, however the impact toughness, elongation and thermal diffusivity decreased to 15 J·cm-2, 6.2% and 33.11mm2·s-1, which were decreased by 25%, 27.9% and 14.5% respectively. With the increase of Zn content, the corrosion current density of as-cast AM60-2%RE alloys was reduced significantly, and the corrosion potential, charge transfer resistance Rct, surface film resistance Rf, compactness of corrosion products were improved, leading to a better corrosion resistance. The corrosion rate was only 0.405 mg·cm-2·d-1 for the alloy with 0.8% Zn addition, which was lower to 36% that of the alloy with 0.2% Zn addition.After 420 ?/3 h+560 ?/8 h solid solution treatment, the mechanical and corrosion propertiesof as-cast AM60-2%RE+x%Zn alloys were improved significantly. The microstructures of solution treated AM60-2%RE+x%Zn alloys were all composed of ?-Mg matrix, Al4 RE, Al11RE3 and a little Al3 Mn. With the increase of Zn,the tensile strength, hardness, impact toughness and elongation of solution treated experimental alloys were increased significantly, however the thermal diffusivity decreased largely. With the addition of 0.8% Zn, the tensile strength, hardness, impact toughness and elongation of solution treated alloys increased to 230 MPa, 54.4 HV, 27 J·cm-2 and 13.7%, which were increased by 16.2%, 3%, 25.6% and 13.2% respectively, compared with the addition of 0.2% Zn alloys, however the thermal diffusivity decreased to 20.495 mm2·s-1, which were decreased by 19.8%.With the increase of Zn content, the corrosion current density of solution treated AM60-2%RE alloys was reduced significantly, and the corrosion potential, charge transfer resistance Rct, surface film resistance Rf, compactness of corrosion products were improved, leading to a better corrosion resistance. The corrosion rate was only 0.113 mg·cm-2·d-1 for the alloy with 0.8% Zn addition, which was lower to 26% that of the alloy with 0.2% Zn addition.After 220 ? /14 h aging treatment, the mechanical properties of solution treated AM60-2%RE+x%Zn were improved, while the corrosion resistance was significantly decreased. The microstructures of solution aging AM60-2%RE+x%Zn alloys were all composed of ?-Mg matrix,Al4 RE, Al11RE3, a little ?-Mg17Al12 and Al3 Mn, without precipitating Zn-containing phase with the other element. With the increase of Zn, the tensile strength and hardness of solution aging AM60-2%RE alloys were increased significantly, while the impact toughness, elongation and thermal diffusivity decreased largely. At 0.8% Zn, the tensile strength and hardness increased to 240 MPa and68 HV, which were increased by 11.6% and 13.3% in comparison with that of 0.2% Zn alloy, however the impact toughness, elongation and thermal diffusivity decreased to 11 J·cm-2, 6% and 41.555mm2·s-1, which were decreased by 26.8%, 35.3% and 8.1% respectively. With the increase of Zn content, the corrosion current density of solution aging AM60-2%RE alloys was reduced significantly,and the corrosion potential, charge transfer resistance Rct, surface film resistance Rf, compactness of corrosion products were improved, leading to a better corrosion resistance. The corrosion rate was0.974 mg·cm-2·d-1 for the alloy with 0.8% Zn addition, which was lower to 51.9% that of the alloy with 0.2% Zn addition. |
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