Study On Microstructure And Corrosion Resistance Of Mg-Al-Sr Alloy

With good creep resistance, high temperature characteristics, and comprehensive mechanical properties, the AJ series alloys, As a new type of Mg alloys, have been applied extensively in automotive, electronic and others industries.But so far, its properties are researched rarely on corrosion resistance. In this paper, therefore, the relationship between microstructure and corrosion resistance of AJ series alloy are evaluated and analyzed seperately. Moreover, some alloying elements were added to improve its corrosion resistance.Mg-6Al-xSr alloy, AJ61+xNd alloy and AJ61+xY alloy, were prepared by "mixture method". the macrostructure and corrosion property of Mg-6Al alloy with various Sr modifier and AJ61 alloys with different content of Nd and Y were assessed by OM,SEM,XRD and EDS. The results show that:1. Sr has refining effect on the microstructure of Mg-6Al alloy, and Al4Sr new phase is formed. As a result, 2.3wt% addition has best refining effect; Al4Sr is distributed along grain boundaries.2. Nd and Y have refining effect on the microstructure of AJ61 alloy. then Al2Nd,Al3Nd and Al2Y,Al3Y new phase is formed separately. As a result, 0.5wt%Nd and 1.5wt% Y addition has best refining effect, and Al2Nd, Al3Nd, Al2Y, Al3Y are distributed both in the grain and grain boundaries.3. The researches about corrosion property and corrosion mechanism were conducted by static weight-loss test, gas collecting test and polarization curve measurement to know the effect of different amount of Sr in the Mg-6Al alloy and Nd,Y in the AJ61 alloy in NaCl solution . The experiment results indicated that 1wt % Sr was benefit to improve the corrosion resistance slightly. On the contrary, Y and Nd had great significance on improving the corrosion resistance. Especially, The alloy with 0.5 wt % Nd or 1.5 wt % Y has excellent corrosion performance.4. The relations between the microstructure and the corrosion properties of Mg-6Al, Mg-6Al-xSr, Mg-6Al-1Sr-xNd and Mg-6Al-1Sr-xY alloys are discussed. The results indicated that theα-Mg grains in Mg-6Al were fined obviously by the Sr addition. But the Sr addition has dual effects to the corrosion properties, accelerating corrosion or inhibiting corrosion, which depends on the amount of Sr addition and distribution of the phases including Sr. Apart from that, combined addition of Sr and Nd (or Y) could not only fine Theα-Mg grains (in Mg-6Al) obviously but also improve The corrosion resistance The reasons are as follows.①R are-earth elements have a high solid solubility which improving the corrosion properties of alloys effectively.②It is obviously that the combined addition of alkaline-earth and Rare-earth elements is good for fine grains. The segregation of Al is inhibited and the overall corrosion properties are enhanced.③The morphology and distribution of rare earth phase make the micro-couple corrosion between grains and grain boundaries more dispersed, and the corrosion resistance is improved.