THE EFFECT OF HYDROGEN ON SHORT FATIGUE-CRACK GROWTH IN AN AL-LI ALLOY

Experimental results are presented to illustrate the degree of susceptibility to hydrogen embrittlement in an Al-Li 8090 alloy. The ductility of the alloy (as recorded in slow strain rate tests) is reduced by hydrogen charging which induces microcrack formation on the surface of the hydrogen treated specimens. Results of fatigue tests show that small fatigue cracks propagate 1.5 to 10 times faster in specimens charged with hydrogen and fractographic evidence shows that short crack growth in hydrogen precharged specimens is transgranular, along persistent slip bands. The effect of hydrogen is reversible, the embrittlement effect being eliminated by holding the specimens for 24 hr at 470-degrees-C.