COMPARATIVE ASSESSMENT OF Al-Si ALLOY GASSING DEGREE WITH THE APPLICATION OF THE ‘FIRST BUBBLE’ AND ‘SOLIDIFICATION UNDER DECREASED PRESSURE’ METHODS

All aluminum alloys in a liquid state are characterised by easy oxidation and absorption of hydrogen from the surroundings (which are the main reasons for casting defects). The amount of hydrogen adsorbed by a liquid alloy depends mainly on temperature and melting time. The performed investigations were aimed at comparing two known methods of measuring a metal gassing degree; the first bubble method and sample solidification under decreased pressure. Liquid metal melting and holding processes were performed under different conditions that caused variability of its gassing degree, resulting in a variability of purity and quality of the liquid metal. The investigations were carried out with using the hypoeutectic aluminum-silica AK7 alloy.