The Research On Micro-alloying Of New Magnesium Alloy AZ63

Magnesium alloy as the lightest structural metal materials has many advantage,such as high specific strength and stiffness, good damping property, easy recyclingand so on. But its strength is so low that limits its application, compared withaluminum alloys and steel. At the same time, the traditional high strengthmagnesium alloys contain a large amout of rare earth elements, having high cost thatalso seriously limits its application. Therefore, it’s very important to develop newlower magnesium alloy with lower cost and higher strength.Based on the strengthening theories of magnesium alloy, a new magnesiumalloy was alloyed using Y, Nd, Sn and Ca, their compositions were optimized byorthogonal test method. The effects of Y, Nd, Sn and Ca concentrations on themicrostructure and mechanical properties of the magnesium alloys were investigated.Simultaneously, the effects of heat treatment on the microstructure and mechanicalproperties were studied. The results indicated:1. The optimized compositons of Y, Nd, Sn and Ca were all0.5%. The ultimatetensile strength, elongation and hardness of this alloy were232MPa, δ=8and70HV,respectively. Its density is ablut1.72g/cm3. This alloy was named AZ63H. Itsultimate tensile strength and elongation were higher than those of the otherMg-Al-Zn-RE alloys.In addition, the concentrations of RE elments were relativelylow i.e., it had low cost and thus had large application potential.2. Some stable strengthening phases of Al-RE phases with short rod-likestructures or particles were formed due to the addition of Y and Nd. At the same time,the grains were refined, and the mechnical properties were improved. But when theconcentrations of RE were too high, some long strip shape structures were formed,which could obviously impair the mechanical properties. Sn could form Mg2Sncompound which distributed at grains boundaries.Their pining role clearly improvethe mechanical properties. The element Ca was mainly solid soluble in the alloy andit can refine grains.3. A proper heat treatment technique for the AZ63H alloy was obtained,solutionized at420℃for30h and water-quenched at room temperature, then theaged at160℃for24h and air-cooled. After the heat treatment, the β phasedecomposed, the dispersive precipitation β’ phase would appear, Mg2Sn phase woulddiffuse into the grain, all of these could lead to the increase of its mechanical properties. The tensile strength, elongation and hardness of the aged alloys were289MPa,11.8%and73.2HV. Compared with the as-cast AZ63alloy, the tensilestrength, elongation and hardness of aged alloys were increased by45.9%,63.8%and7.6%. Compared with the as-cast AZ63H alloy, the tensile strength, elongationand hardness of aged alloys were increased by24.5%,47.5%and4.5%.