Investigation On Microstructure, Elevated-temperature Tensile Properties And Behavior Of Frictional Wear Of Magnesium Alloy Tube

As a light and green material with latent capacity of development in the 21 century,magnesium alloys became more and more popular within the material field. Although it is awidely used magnesium alloy, mechanical properties of magnesium alloy AZ91D at elevatedtemperature was not good enough. Several means were adopt to enhance the tensile propertiesof magnesium alloy at elevated temperature: alloying reinforcement by adding multipleelement RE and Ca, development a new Mg-Al-Zn series alloy with increasing the content ofZn, both die cast and spray deposition forming were used to made up the extruded ingot,isothermal extrusion was used to produce the magnesium tube. Tensile properties at room andelevated temperature were studied. Properties of frictional wear of three kind of magnesiumalloy were studied at the same time.Results show that, microstructure of AZ91D+RE+xCa (x=0.5%, 1%, 1.5%) magnesiumtube were build up by phases ofα-Mg, Mg₁₇Al₁₂, Mg₂Ca, Al₁₁La₃. With increasing of Ca,unfavourable influence was brought into the properties at elevated temperature by changing ofsecond phase from graininess to strip-shape. All of the tubes got ultimate tensile strengthσ_b(UTS) greater than 200MPa, with the best ofσ_b 225.2MPa of AZ91D-RE-0.5%Ca magnesiumalloy.With increasing Zn and reducing Al and adding Ca, microstructure of Mg-8Zn-4Al-xCamagnesium alloy was build up with new tiny intermetallics instead of coarse aberratedeutectic Mg₁₇Al₁₂. Plastic working of magnesium alloy was possible at 150℃～200℃, becauseelongation increased with the increasing of temperature. Tensile properties of AZ91D+Ce+Camagnesium alloy tube with spray deposition ingot were high at room temperature but low atelevated temperature. T6 and T5 heat treatment were adopted to enhance the properties atelevated temperature. UTS and YS were enhance a lot after T6 treatment at 200℃, elongationof as-extruded and tube after T5 treatment were better than the others. Plastic working of as-extruded and T5 treatment magnesium alloy tube were possible at 200℃. UTS and YS oftube after T5 treatment were both better than the as-extruded robe.Performance of friction wear of AZ91D and AZ91D+RE+Ca magnesium tube with diecast ingot and AZ91D+Ce+Ca magnesium tube with spray deposition ingot were studied. Theresults show that, in low rate of revolutions, friction coefficient and wear rate of AZ91Dmagnesium tube with die cast ingot were lower than the others. Oxidative wear plays animportant role in AZ91D, when oxidative combining with abrasive particle wear in the othertwo alloys. In high rate of revolutions, performance and state of friction wear ofAZ91D+Ce+Ca magnesium tube with spray deposition ingot was better than the other twoalloys.