Study Of Tribological Properties Of AZ80A,ZK60A And ME20M Magnesium Alloys

Magnesium alloys are widely used in many fields,such as aerospace,cars,arms,electronics and so on.Due to poor wear resistance,it is easy to occur friction damage in the service process.Therefore,it is very important to study the tribological properties of magnesium alloys.In this paper,AZ80A,ZK60A and ME20M magnesium alloys,which are widely used,are selected as the research object.The reciprocating ball-disk friction method is used to systematically study the magnesium alloy under different test environments,which include sliding speeds,loads and temperature conditions through matching with GCr15 steel balls.The wear mechanism of magnesium alloy is explored to provide theoretical basis for the industrial application of magnesium alloy.Under dry friction conditions,when the load is 6 N,the dry friction coefficient of magnesium alloy increases first and then decreases with the increase of speed,while the wear rate decreases is opposite.At a speed of 0.1 m/s,the dry friction coefficient and wear rate of the magnesium alloy gradually decrease with the increase of load.The reason is that a lot of friction heat are generated during the dry friction process with the speed and load increasing.On the one hand,the mechanical properties of the surface layer of the material are reduced so that the ductility is improved.On the other hand,frictional heat oxidizes the worn surface to form a friction oxide layer,which reduces the contact between friction pairs and improves the wear resistance of the alloy.As the test conditions change,the wear mechanism of magnesium alloys gradually changes from abrasive wear and oxidative wear to fatigue spalling and slight plastic deformation.In the environment of oil lubrication and aqueous environment,when the test conditions are the same,the friction coefficient and wear rate of magnesium alloys are basically similar to dry friction,while the wear mechanism is different.Under oil-lubricated conditions,the wear mechanism of magnesium alloys is mainly abrasive wear and slight delamination wear,there is not oxidative wear and plastic deformation.During the friction process,the oil film not only isolates the air but also protects the material.Therefore,it is difficult to form an oxide film on the friction surface.However,in the oil-lubricated state,the formation of an adsorbed oil film between the two contact surfaces significantly reduces the friction coefficient and wear rate,and its effect is similar to the oxide film.In an aqueous medium environment,the wear mechanism of magnesium alloys is mainly abrasive wear and corrosion fatigue spalling.As the speed and load increase,the corrosion effect of the aqueous medium on the magnesium alloy is more obvious.The reason is that the aqueous medium has a certain corrosion effect on the magnesium alloy,which reduces the surface fatigue strength of the material.On the other hand,as the speed and load increase and the worn surface scratches,the aqueous medium penetrates into the cracks and grooves of the surface layer,which are more likely to cause corrosion to the alloy.Once the corrosion occurs,it will propagate into the interior of the material,causing delamination of the surface metal.In addition,under the environment of aqueous environment,the frictional heat will be significantly reduced and it is not easy to accumulate.As a result,the degree of oxidative wear will be weakened or even disappear.When the temperature is 25 to 200 degrees,the speed is 0.15 m/s and the load is 6 N,the friction coefficient of magnesium alloys tends to decrease first and then increase and then decrease as the temperature increases.However,the change trend of wear rate is different,the reason is that the relative resistance of the oxide layer on the worn surface to the softening of the matrix when the temperature increases.As the temperature increases,the wear mechanism of magnesium alloy gradually changes from abrasive wear and oxidative wear to fatigue spalling and plastic deformation.The reason is that the plastic deformation ability of the magnesium alloy is enhanced as the temperature increases.At the same time,the increase of temperature also makes the adhesion between the oxide layer and the alloy matrix poor,leading to the destruction of the oxide layer and the inability to protect,so that the alloy wear mechanism changes.During the friction and wear test of magnesium alloy,it is found that AZ80A magnesium alloy showed good tribological properties in different friction environments,which is attributed to the following aspects:(1)AZ80A magnesium alloy has higher hardness.(2)The second phase?-Mg₁₇Al₁₂ hard phase in the alloy plays a good supporting role.(3)?-Mg₁₇Al₁₂ has a certain stability in a wide PH range,so that the alloy acts as a barrier during corrosion.(4)The oxide layer formed on the worn surface of AZ80A magnesium alloy during friction has a certain lubricating effect.(5)Within a certain temperature range,the thermal stability of the second phase?-Mg₁₇Al₁₂ of the AZ80A magnesium alloy is relatively good.