The role of advanced corrosion research methods for Magnesium alloys in automotive applications

The guide direction today is reduction of vehicle weight and saving of fuel consumption. Magnesium is the lightest of all the commonly used metals and is very attractive for applications in automotive industry. However, environmentally assisted fracture significantly decreases the fatigue and creep resistance, mechanical stability and durability of high-strength Mg alloys. For example, such magnesium applications as wheels, transmission housings, pedals, etc. require good fatigue resistance in corrosive atmosphere. In order to produce parts for the automotive industry it is necessary to develop alloys with formability and durability in active environments. Until recently, corrosion resistance and creep resistance have been considered to be the main issues for long-term durability, reliability and applicability of Mg-based structural materials. These problems traditionally have been separated as corrosion behavior in non-stressed states and creep in non-corrosive conditions. In recent years the importance of environmental effects in many types of fracture processes has been recognized and it seems worthwhile therefore to examine more closely the role of environment in creep rupture as combined stress-environmental effects. So, the investigation of environmental assisted creep is very important as a tool to discover a mechanism of processes going in the tip of a crack and as the phenomenon very influencing mechanical stability of alloys in real service conditions. However, mechanical and corrosion processes develop simultaneously in real environment conditions, and inevitably lead to the appearance of new synergistic effects which significantly reduce the lifetime of Mg-alloys. Corrosive environment (3.5% NaCl) significantly decreases fatigue life of die-cast and extruded Mg-alloys (AZ91D, AM50, AZ31, etc.). Extruded alloys show a higher sensitivity to the action of NaCl solution in comparison with die-cast alloys; however, their corrosion fatigue life is longer than that of die-cast alloys. Besides dynamic (high cyclic) corrosion fatigue, we have studied static corrosion fatigue which we called corrosion creep. The last one is of great industrial importance especially for Mg alloys because their low creep resistance. It is aimed to design new Mg alloys using the microstructure, electrochemical properties and failure analysis under static and dynamic loading in order to achieve the goal of achieving stable mechanical properties including good ductility. This paper will present some technological methods directed to improve magnesium-alloys resistance in active environment are proposed. The results will point out the know-how and experiments of die cast, extrusion alloys. The focus is on the evaluation of the stress corrosion behavior in alloys of various compositions and size effect in order to optimize the choice and design of alloys with elevated resistance to stress corrosion. The final aim is to prove correlation between the microstructure and advanced corrosion methods for developing new magnesium alloys applications using Die cast, Extrusion and Semi-Solid components.