Effect Of Sc Addition On Mechanical And Corrosion Resistance Of Al-Mg Alloy

Al-Mg alloys have been widely used for automotive,aerospace and marine areas because they exhibit excellent strength,elongation,formability,corrosion resistance and low density.However,it can become susceptible to corrosion when Al-Mg alloys are exposed to temperatures range from 50℃～220℃ for long period.This phenomenon is known as “sensitization”.How to r improve the corrosion resistance of Al-Mg alloy is the current research focus of Al-Mg alloy.Scandium(Sc)was discovered as addition to modify microstructures and improve performance of the aluminum.Some research reported that Sc has a strong effect on the grain size and second phase of aluminum alloys.Meanwhile the corrosion resistance of aluminum alloys is affected by the shape and distribution of second phase and grain size,etc.Therefore,it is significance to study the effect of Sc addition on the corrosion resistance of Al-Mg alloy.This paper compares the Al-Mg and Al-Mg-0.1Sc(0.1wt.%)properties and studies the effect of Sc addition on the corrosion resistance and mechanical properties of Al-Mg alloy.The effect of recrystallization on the corrosion of Al-Mg alloy is also studied.The results are as follows:(1)Adding 0.1wt% Sc to Al-Mg alloy can effectively refine the grain size of the ingot and reduce the macro segregation of the ingot during the cooling process.For rolling sheets,the addition of Sc can significantly increase the recrystallization temperature.The Al-Mg alloy begins to recrystallize at 260 °C and finish recrystallized at 290 °C.However,the Al-Mg-0.1Sc alloy cannot be recrystallizing completely even at 550℃.Therefore,the Al-Mg-0.1Sc alloy can still maintain high strength and hardness after high temperature treatment.(2)The cold-rolled Al-Mg and Al-Mg-0.1Sc alloy both show excellent corrosion resistance.The annealed(300℃-2h)Al-Mg alloy has slight intergranular corrosion(IGC)with a corrosion depth of around 10μm.The annealed Al-Mg-0.1Sc alloy did not have obvious IGC.The corrosion resistance of cold-rolled Al-Mg alloy is better than annealed Al-Mg alloy.The Al-Mg-0.1Sc alloy maintains excellent corrosion resistance in both cold rolled and annealed conditions.(3)The cold-rolled Al-Mg alloy that was sensitized(175℃-20h)has IGC with a corrosion depth of around 10 to 15μm.The annealed(300℃-2h)Al-Mg alloy that was sensitized(175℃-20h)has IGC with a corrosion depth of around 80 to 100μm.It shows that sensitization is the key factor that deteriorates the corrosion resistance of Al-Mg alloy,and the sensitivity of “sensitization” of annealed alloy is significantly higher than that of the cold-rolled alloy.(4)The cold-rolled Al-Mg-0.1 alloy that was sensitized(175℃-20h)has no IGC.The annealed(300℃-2h)Al-Mg-0.1Sc alloy that was sensitized(175℃-20h)has slight IGC with a corrosion depth of around 10 to 20μm.It shows that Al-Mg-0.1Sc alloy contains better corrosion resistance compare with Al-Mg alloy.(5)Corrosion test for Al-Mg alloys of different recrystallization degrees show that the intergranular corrosion degree increases with the degree of recrystallization.