ACOUSTIC EMISSION AND HYDROGEN EVOLUTION DURING SOLIDIFICATION OF ALUMINUM ALLOYS

Study of the solidification process of both Al-Si and Al-Cu alloys proved the presence of acoustic emission phenomena.Two peaks of count rate have been observed.The total counts of both peaks increase with the increasing hydrogen content of the alloy.The mechanism of producing the acoustic emission has been discussed.At the same time,results obtained by oth- er techniques strongly support the good correlation between the acoustic emission and hydrogen releasing during solidification.The bubble nucleation between dendrite arms is the main cause of the first peak,while the fracture of the bridge connecting the interdendrites at the later stage of solidification is the main cause of the second peak.It is probably due to the hydrogen evolution and accumulation to create high pressure in the interdendritie region.