Vacuum effects on fatigue properties of magnesium and two magnesium alloys.

Abstract

The effects of a high-vacuum environment and of vacuum outgassing time on the fatigue properties of unalloyed magnesium and of magnesium-thorium and magnesium-lithium alloys under constant-load, reversed bending (30 cps) were studied. Tests were run, all at room temperature, at atmospheric pressure and at various pressure levels down to 10 ~8 torr. The S-N curves for all three metals show significant increases in their fatigue properties in vacuum; typically, at 10 7 cycles, the increases in fatigue limits were approximately 45% in vacuum over those in air. Also, at an outer fiber stress equal to the yield stress of the material, for example, fatigue lives increased by factors of 3, 5, and 12 for magnesium-lithium, magnesium, and magnesium-thorium, respectively. Prolonged outgassing prior to fatigue testing had no significant effect on the vacuum fatigue properties of any of the metals studied in this investigation. For the conditions of these tests, the critical pressure range below which fatigue properties are increased was established at 0.1 to 1 torr for commercially pure magnesium. Two possible explanations of the increase of fatigue properties of metals in vacuum environment over those in air are discussed, and the experimental evidence supporting each is evaluated.

Corrosion Fatigue of High Pressure Die Cast Magnesium Alloys

“…The results of fatigue tests in seawater for coated and un-coated AZ91D and AM50 show that the special coating and coating & sealing ('Anomag') do not decrease the fatigue properties in the seawater environment (see figures 5 & 6). It has been noted that magnesium coating treatments, which are applied for corrosion protection, usually decrease the fatigue and corrosion fatigue resistance of materials in air, but not in seawater [15].…”