Mechanical Properties and Machinability of Magnesium Alloy AZ31 and AZ91 – A Comparative Review

Abstract

Throughout the last decade magnesium alloys have slowly overtaken aluminium alloys, especially in the automotive and aerospace industry. Due to its attractive weight-resistance and weight-hardness characteristics, the global production of Magnesium alloys has grown from 360,000 tons in 1999 to 850,000 tons in 2013. Magnesium alloys AZ91 and AZ31 are the most widely used grades. AZ 91 exhibits a Knoop’s hardness (HK) of 76.2 that is higher to the AZ31 with a 51.1 HK. The manufacturing of AZ 91 is through a casting process whereas AZ31 is manufactured by using an extrusion process. The microstructure of AZ31 and AZ91 are highly influenced by the heat generated during the machining process that also affects the surface hardness due to the high thermal conductivity of the material that range from 62 W/m.k to 96W/m.k. Both materials have a very good machinability where milling, drilling, and turning are commonly used. However, extreme care should be taken in terms of machining conditions as Magnesium alloy is highly flammable. However, a safe machining process can be performed by avoiding very fine chips, magnesium dust and also the usage of water-based coolants that react with the raw material. This paper has widely reviewed the studies that have been conducted since the evolution of magnesium alloys in terms of machining parameters, machining consumables and their effect on the mechanical properties, surface conditions and limitations of the various machining processes.