The study on microstructure and properties of thermal-sprayed coatings on magnesium alloy
Bi Wenyuan
CNKI
Abstract
Magnesium is very rich in reserves on the earth, but it isn’t widely used. With the depleting reserves of many metal elements on the earth today, the sufficient development and utilization of magnesium resources can ease the pressure on the metal element consumption.Magnesium alloy, aluminum alloy and steel are known as the three structural metal materials,and magnesium alloy is the lightest one. Magnesium and magnesium alloy have many advantages, such as high specific strength, high specific stiffness, good electrical conductivity, and good thermal conductivity and so on. What’ more, magnesium alloy is good properties in cutting and they can be reused by some simple treatment, as a result, they cause the concern by the experts. Because of the advantages above all, magnesium alloy has been partially used in automobile manufacturing, electrical and electronic industry and so on, and it possibly has wide application prospects in transportation, aviation, aerospace and defense industry in the future. However, magnesium alloy has its own shortage in the using process. The main problem is that the chemical property of magnesium is active and the bad wear-resistant performance. The shortages mainly reflect in the following two aspects, it can be oxidized in the moist air and be worn seriously when it isn’t loaded. The two shortages of magnesium alloy have severely restricted the application of magnesium alloy. To solve the problems, many scholars have taken a lot of researches at home and abroad. There are two main solutions, one is adding alloying elements, and the other is surface modification. Many developed countries improve the overall performance using the surface protection method,such as a variety of surface coatings, micro-arc oxidation treatment and chemical conversion film. However, the methods above all have their own inherent limitation. For example, the chemical conversion film cost is high, electroplated coating has the problem of environmental pollution.
This study uses the method of thermal spray to prepare the coatings on the surface of magnesium alloy. The microstructure and properties of arc-sprayed Al coating and plasma spraying Al/Al2O3
composite power coating are investigated. At the same time, the property of plasma spraying Al/Al2O3 composite power coating is compared with the arc-sprayed Al coating.Plasma spraying uses the rigid non-transfer plasma arc as the heat source, and uses theinert gas (Ar) as the shielding gas. The mixed powder is accelerated and it impacts the surface of the base metal in a high speed resulting that the coating is formed. Plasma spraying has many advantages, such as high flame stream temperature, concentrated energy,high density and so on. The purpose of the study is to improve the performance of magnesium alloy using the plasma spaying technology. Coating on AZ31B magnesium alloy surface is obtained by electro-arc spraying in order to improve the bonding strength. Based on the wear test, whether the wear volume or the weight, the base material of Magnesium alloy has maximum value, Al coating has a lower value, and Al/Al2O3 composite power
coating has the minimum value. It is found from the microstructures of the coating made of specific parameters that coating have metallurgical bond region.It can be found according to the analysis of the coating that the coating which the base material of Al and reinforced phase of Al2O3 particles is the optimal choice for improving the performance of magnesium alloy. The research can supply the theoretical basis for improving the comprehensive properties of magnesium alloy in future.
Keywords:Magnesium alloy, Thermal spray, Bonding strength, Microstructures and properties
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