Evaluation of defects in aluminium piston casting by using ultrasonic and computer tomography

摘要

Pistons used in the automobile engines are made of aluminum alloys, and endurance of high pressure and high temperature are required. In recent years, high strength pistons are needed for increase of pressure temperature in the engine cylinder room. High strength piston is possible when the piston casting has few casting defects, such as micro-pores and cracks. Generally the defects can be evaluated by non-destructive test (NDT), but the most efficient ways for evaluation are using ultrasonic and computer tomography. In the present study, two NDT methods were compared and evaluated to investigate the defects in the aluminium piston castings. Artificial defects were machined by using a very small drill with a diameter of 1 mm, 0.5 mm, 0.3 mm, 0.2 mm and 0.1 mm, respectively. The defects were investigated by using ultrasonic tester and computer tomography system. Defect smaller than 0.3 mm may not be found by using ultrasonic test, but the defect may be found by using computer tomography system. The conditions for investigation on detecting small defects are discussed in the present study. The scanning time for in-line defect analysis is also discussed.