Effect of liquid nitrogen assisted milling on AZ91 magnesium alloy

Abstract

The objective of the present work is to study the effect of liquid nitrogen (LN2) cryogenic on the performance of face milling for producing quality surface in AZ91 magnesium alloy. Machining AZ91 alloy has been a challenging domain due to the risk of ignition or spark during machining, which affects surface finish. In this study, face milling is carried using uncoated carbide inserts in cryogenic condition, and the performance is compared with dry condition based on the surface integrity (SI) characteristics. The findings of this study reveal that use of LN2 results in enhanced surface integrity. Observations showed no harm to alloy microstructure in both conditions, with no alterations to grain integrity in the near machined area. Cryogenic machining resulted in reduction in machining temperature ranging from 146.7 ⁰C to 178.5 ⁰C, when compared to dry condition temperature ranging from 219.4 ⁰C to 251.2 ⁰C. Cryogenic machining considerably generated smoother (Ra=0.0606μm) and harder (HV=116.5) surfaces, and also resulted in compressive residual stresses. This study concludes that cryogenic-assisted milling is an excellent alternative for the production of superior-quality surface in AZ91 alloy.