Analisis pengaruh temperatur dan waktu penahanan age hardening terhadap kekerasan dan struktur mikro pada piston bekas paduan Al-Si-Cu-Mg yang dicor ulang pada temperatur penuangan 700 oC

Abstract

Use of aluminum alloy is increasing from year to year. This can be seen from the order of usage of aluminum alloy which ranks second after the usage of iron or steel, and the first the usage for non ferrous metals. Aluminum alloys are often used in automotive parts such as pistons, engine blocks, cylinder head, valve and so forth. The use of aluminum alloys for automotive components are required to have good strength. On the other hand, the production of vehicles in Indonesia is increasing so much the piston is not feasible using discarded into the waste. Therefore it is necessary to recycle the used pistons processing and can be used back on the vehicles. This research was done through by team work, there are divide the study into three discussion. The discussion include discussion about the making of the piston with cast techniques, analysis of the mechanical strength in the piston with addition insert in the piston ring groove, and the process of heat treatment on the piston so as improve its mechanical properties. This research will discus heat treatment about the influence of temperature and holding time on the heat treatment process of precipitation hardening alloys of Al-Si-Cu-Mg made by melt piston and former ADC 12 with mass ratio 50%;50%, at the pouring temperature of casting is 700 oC. The precipitation hardening process was done by variation of the aging temperature 100, 155, and 200 oC also the holding time 2, 4, and 5 hour. The results show that the alloy Al-Si-Cu-Mg is casted without heat-treatment process have an average hardness is 60.2 HRB. And for the alloy Al-Si-Cu-Mg, which have gone through the process of solid solution and quenching hardness value decrease to 46.75 HRB. While the alloy Al-Si-Cu-Mg, which have gone through the process of artificial aging hardness value increase is 82.5 HRB. The iincreasing in the most optimal hardness value is obtained when the aging temperature of 200 oC with holding time is 5 hours of 82.5 HRB than the increasing hardness on the aging temperature of 100 oC is only 71.5 HRB and aging temperature of 155 oC is 82 HRB with the same holding time. The temperature and holding time on the aging affects the microstructure which forms the higher the temperature used and the longer the detention time in the aging process so the result of precipitate will increase and grew up to achieve the most optimal condition on the precipitate growth of Al-Si-Cu-Mg alloys. With the growth of the precipitate will inhibit many dislocations that will affect the increase in hardness of Al-Si-Cu-Mg alloys.