Surface layer modification by cryogenic burnishing of Al 7050-T7451 alloy with near ultra-fine grained structure

Burnishing has been increasingly utilized to improve the surface integrity of manufactured components. The generation of surface and subsurface layers with ultrafine grains, attributed to severe plastic deformation and dynamic recrystallization, leads to improved surface integrity characteristics including surface and subsurface hardness and reduction in surface roughness. Additionally, due to the generation of compressive stresses within the refined layers, increase in fatigue life and improved wear and corrosion resistance can be achieved. In this study, we apply cryogenic burnishing on Al 7050-T7451 discs and compare the surface integrity characteristics with dry conventional burnishing. A special roller burnishing tool with flexible rotating roller head was designed and used to perform the cryogenic burnishing experiments using liquid nitrogen as the coolant. The results show that cryogenic burnishing can increase the surface hardness by an average of 20-30% within a layer depth of 200 μm compared to only 5-10% increase using dry conventional burnishing. Refined layers with nano grain structure were also generated. During cryogenic burnishing the tangential burnishing forces were higher than those of dry conventional burnishing due to rapid cooling and work hardening of the material.

Critical review on different burnishing processes of Ti-6Al-4V Alloy

Titanium and its alloys are the most commonly and most widely used due to its significant properties like good biocompatibility , good tensile strength , low density , and good creep property up to 300 degrees centigrade .It is used in the major engineering fields like civil engineering , nuclear engineering , aerospace engineering etc. Surface finish of the titanium material plays a prominent role in influencing its functional characteristics like wear resistance, fatigue strength, corrosion resistance and power loss due to friction. In normal machining methods like turning, milling or even classical grinding can’t meet the desired surface finish. To overcome this one of the method employed is burnishing, which is very simple and effective method for improvement in surface finish and can be carried out on lathe machine. The latest innovate technique used in the burnishing is the cryogenic burnishing in which the liquid nitrogen is supplied as the coolant. This work deals with study of different burnishing processes of titanium alloy Ti-6Al-4V.