Magnesium alloys have been widely used in automotive, aerospace and electronic industries due to their unique properties such as high strength-to-weight ratio, high corrosion resistance and low cost. Magnesium alloys are getting more attention these days because of the increasing demand for light weight materials in the automobile and aerospace industries. Increasing fuel efficiency has become a target of government and industry interests, which is driving the development of advanced lightweight materials and components.
Surface treatment plays a crucial role in enhancing the performance of magnesium alloys in any application, especially in exposed environments. The most common surface treatments used on magnesium alloys are conversion coating, anodizing, electroplating, passivation, coating and hard anodizing. Each of these treatments can be used to improve the performance of magnesium alloy in some way.
Conversion coatings are chemical treatments used for protection of the metals from corrosion and increasing the surface hardness. The most widely used conversion coatings for magnesium alloys are chromate conversion coating (CCC) and phosphate conversion coating (PCC). CCC provides a good barrier between the magnesium and its environment, thus providing an excellent corrosion protection. PCC helps in improving the wear and corrosion resistance of magnesium alloys.
Anodizing is a popular treatment for magnesium alloys. Anodizing involves the application of an electric current to the surface of the metal, which causes oxidation of the uppermost surface layer. This oxidation layer forms a protective barrier against corrosion and wear. Anodizing of magnesium alloys can be done in two different ways, i.e., type I and type II anodizing. Type I anodizing provides a thick oxide layer that is resistant to abrasion and corrosion, while type II anodizing provides a thin oxide layer that is wear resistant.
Electroplating involves the application of metal or alloy plating onto the surface of the metal. The aim of electroplating is to increase the surface hardness and wear resistance of magnesium alloys. Electroplating can be done in two different ways, i.e., galvanic (electroplating with through-holes) and electrolytic (electroplating without through-holes). It is important to select the appropriate metal for electroplating in order to get the desired results.
Passivation is the process of protection of the surface of a metal by the formation of an oxide layer. It helps to improve the corrosion resistance of magnesium alloys by preventing the penetration of corrosive substances into the metal surface. Passivation of magnesium alloys is done by applying a mild acid to the metal surface followed by rinsing.
Coatings involve the application of organic or inorganic materials on the magnesium alloy surface in order to improve its performance. The two most commonly used coatings are organic coatings and metal coatings. Organic coatings provide both protection to the surface and decoration, while metal coatings provide protection to the surface and enhance its hardness.
Hard anodizing is a non-electrolytic process for increasing the wear resistance of magnesium alloys. This process involves the alkaline etching of the metal surface followed by the application of a hard film of aluminum oxide onto the alloy surface. This hard film is highly wear-resistant and provides excellent protection to the alloy against corrosion and wear.
In summary, there are a variety of surface treatments that can be used on magnesium alloys in order to improve their performance. Each treatment has its own advantages and limitations and must be chosen according to the application. It is important to choose the appropriate surface treatment in order to meet the desired performance requirements.
