Embrittlement properties of aluminum alloys 7075 and 6061 in high-pressure gaseous hydrogen

Abstract

SSRT (slow strain-rate technique) tests were carried out using smooth- or notched-tensile specimen of aluminum alloy plates 7075-T6 and 6061-T6 in gaseous hydrogen under high-pressure 70 or 85 MPa, as compared with in 90% relative humidity air under atmospheric pressure. For 7075 the humid air caused a significant embrittlement, leading to intergranular cracking, while in contrast the high-pressure hydrogen gas resulted in little embrittlement, where the transgranular fracture mode attributed to hydrogen effect was however observed, showing an enhancement of void coalescence. The result indicates that high-pressre gaseous hydrogen is much less severe to provide hydrogen to aluminum materials than humid air. On the other hand, 6061 was found to be immune to hydrogen embrittlement in either environment. It was then comprehended that the aluminum alloys represent- ed a series of change in fracture mode from transgranular to intergranular with increase in hydrogen concentration.