Characterization of surface, subsurface and their effect on fatigue life after machining on Aerospace Grade Aluminum Alloy (Al 6082-T6)

Abstract

Aluminum alloys are widely used in automotive and aerospace industry due to their lower mass to strength ratio than other metallic alloys. Apart from their inherent properties, aluminum alloys like other metallic alloys shows significant change in their mechanical properties like fatigue, hardness etc. according to the machining parameters like speed of cut, nose radius of tool, coolant, feed rate, etc. that relates to the change in grain structure. Knowledge of optimized parametric selection is very important in machining of aluminum alloys in context of their mechanical behavior. In this research, the effect of different machining parameters on the subsurface of aerospace grade aluminum alloy (Al-6082-T6) was observed. Feed rate, cutting speed and depth of cut were the key machining parameters that were considered. The main result focused was the depth of subsurface damage caused by these machining parameters. ISO 3685 was followed for selecting cutting parameters and their range was selected by tool manufacturer’s catalogue i.e. Sandvik Coromant Catalogue 2011 and Corokey of the Sandvik Coromant Catalogue 2011. All of 27 samples, according to Design Expert software, were prepared on CNC machine with 3 of variable values of cutting speed, feed rate and depth of cut. These samples were prepared for metallography by mounting, grinding, polishing and etching. ISO 4287:1997 is followed for surface roughness parametrical study. According to ASTM E384 and E92 micro hardness tests were carried out down the edge of the cross section of sample. Results of surface roughness and micro hardness tests are compared with fatigue life. Results are discussed along with recommendations for optimized machining parameter to achieve desirable mechanical properties of material (surface roughness, subsurface hardness and fatigue life).