Evaporation of Mg from Al-Mg alloys in molten state under reduced pressure

Abstract

The behavior of Mg evaporation from Al-(3-12%) Mg-(0-0.01%) Be alloys during heating under reduced pressure was investigated by the differential thermal analysis and thethe measurement of pressure in a closed vessel. When the content of Mg was higher, the evaporation happened under higher pressure in vessel and at lower temperature than when the content was lower. The addition of Be had effects of inhibiting Mg evaporation.
The evaporation of Mg from pure Al-5% Mg-(0-0.01%) Be alloy and Al-10%-(0-0.01%) Be alloy under reduced pressure after holding at 725 or 715°C for 0-60min. was investigated by the same method as previous. The relation between the holding time of the melt and the limit value of reduced pressure was studied. The limit values of reduced pressure for the above both alloys were larger (i.e., lower pressure) when the content of Be was lower and the holding time was longer (at least more than 15min.). The limit value of reduced pressure for these alloys, containing more than 0.004% of Be, was lower than 0.7mm Hg. The results obtained by commercial Al-(5 or 11%) Mg-(0.005%) Be were nearly the same as those by pure alloys.