Minimum quantity lubrication and heat-assisted friction drilling of AA7075-T6 aluminum alloy

In this study, friction drilling was performed for AA7075 - T6 alloy under dry, minimum quantity lubrication (MQL), heat, and heat + MQL process environments. The aim is to achieve the optimum bushing profile by increasing the productivity of friction drilling in different process environments. Friction drilling experiments were carried out at constant speed and feed rate; the effects of the drilling environment on thrust force, temperature, hole bushing profile geometric properties, hole surface quality, thread stripping strength, and micro hardness values were investigated. The test results revealed that the drilling environment directly affects the formation of heat and thrust forces during the process. The best surface roughness (Ra) value was achieved in the heat environment with 2.61 µm. Thread stripping experiments showed that the heating process improved the thread stripping strength of AA7075-T6 by 14.65% when compared with the dry environment. The results revealed that the main damage mechanism occurred in the transition zone from the heat-affected zone (HAZ) to the base material (BM) in the tensile strength test on the heat process environment specimen, while the roots of threads were affected in other process environments. The different microhardness values were measured in the thermo-mechanically affected zone (TMAZ), HAZ, and BM formed during the process.