Effects of Degassing Conditions in Fabrication Process on Hydrogen Content of High Strength P/M Aluminum Alloy Made from Alloy Powder

Abstract

Effects of degassing conditions on hydrogen content and other properties of a P/M 7091 alloy were studied. The green compacts of the alloy powder were encapsulated and vacuum-degassed with various conditions, and then hot pressed and rolled. The degassing conditions were changed within 653-793 K in temperature, 0.3-24 h in time, 2.1-2.4 g/cm³ in green density and 10⁰-10^-5 Pa in degree of vacuum. Results obtained were as follows:
1) The hydrogen content of 7091 alloy powder was about 55 p.p.m. And that of a P/M billet made from 7091 alloy powder without vacuum-degassing was close to 40 p.p.m.. Therefore the billet included a number of residual pores at the boundaries between powder particles.
2) Hydrogen contents of the hot pressed P/M billets and rolled P/M sheets decreased with increasing the degassing temperature and the time. The P/M materials made through degassing at 653 K for I h contained about 5 p.p.m. hydrogen, and through degassing at 773 K for I h and for 24 h, contained about 1.2 p.p.m., 0.6 p.p.m. respectively. The P/M sheets were pore free even when they had high hydrogen content about 5 p.p.m.. Hydrogen contents of the P/M 7091 alloy sheets were in 0.6-5 p.p.m., which were higher than that of a I/M 7075 alloy sheet of 0.11 p.p.m..
3) Effects of both the green density and the degree of vacuum at degassing on the hydrogen content of the P/M billets were little, excepting the fact that the higher green density of 2.4 g/cm3 resulted in slightly high hydrogen content.