الفهرس | Only 14 pages are availabe for public view |
Abstract Friction drilling is used to process special holes with a bushing and a boss in thin sheet metals without producing chips via a non-traditional tool-drill. Friction drilling parameters involve the feed rate, rotational speed and profile dimensions of the drilling tool, which directly affect the induced bushings dimensions, as well as, the microstructure of the produced hole. In the present study, friction drilling parameters were manipulated during the performance of friction drilling of 6082 and 7075 Al-alloys, the length, width, and thickness dimensions of the sheets are approximately 100, 50, and 4 mm, respectively. It was drilled by friction using tool cone angles with values of 40, 45 and 50⁰ under different feed rates (100, 200 and 315 mm/min) and rotational speeds (1000, 1250 and 1600 rpm). Moreover, the temperature variation in the tool-work-piece interface was recorded during the drilling processes via an infrared camera and four thermocouples located at different positions near the drilling zone. The characteristics of the thermally induced bushes (shape, dimensions, and surface roughness) were inspected. Furthermore, in the present study, the microstructure evolution and hardness distribution in the thermally-formed bush and in the heat-affected zone around the bushing with and without heat treatment were premeditated. Corrosion tests were carried out to evaluate the corrosion resistance of friction drilled hole for different conditions. During the formation of the bushing and the boss in the investigated aluminum sheet metals, the minimum measured temperature was 220 °C and the maximum measured temperature was 380 °C. It was found that the temperature in the tool-work-piece interface increased with the reduction of the feed rates and the increase of both of the rotating speeds and the tool cone angles. It was found that higher temperature resulted in greater bushing heights and smaller bushing thickness. No systematic effect of process parameters was observed on resulting hole diameter and boss height. Furthermore, the surface roughness of the drilled holes were found to be increased with the increase of the rotational speeds and lower feed rate.It was found that the hardness of the bush was slightly increased with increasing of the tool cone angle and reduction of the tool rotational speed. However, the hardness of the thermally-induced bush showed values lower than the parent metal. The hardness values increase with moving away from the edge of the induced bush. The hardness near the drilling surface was approximately 65±10 HV, while it recorded hardness values of 75±10 HV at 5 mm away from the drilling surface. In addition, the microstructure of the friction drilled specimens showed a very fine structure in the drilling zone due to crushing of the original structure during the friction drilling process. The thermal cycle of friction drilling resulted in a reduction of micro-hardness. The softening phenomenon of 6082 and 7075 AL- alloys is due to the dissolution or coarsening of the strengthening precipitates. The hardness of aluminum is improved by artificial ageing, the hardness increases to 145±15 HV after artificial ageing. Consequently, a performance of a heat-treatment of the friction drilled 6082&7075 Al-alloys are required to ensure a homogenization of the produced structure. The result is obvious that there is an improvement in pitting corrosion of Al- alloys (BM 6082&BM7075) after drilling process. The obtained results, as shown by SEM, reveal the dangerous growth of localized attack of the BM alloys surfaces in 3.5% NaCl solution. Ageing treatment improved corrosion resistance of friction hole drilled for 6082 Al-alloy. After heat treatment, Mg2Si precipitates are more concentrated in the α-Al matrix, resulting in increasing corrosion resistance. |