Effect of hydrogen accumulation on θ' precipitates on the shear strength of Al-Cu alloys

Abstract

We investigate the effect of accumulation of H atoms on θ' strengthening precipitates in Al-Cu alloy. A relationship is established between the H accumulation and decrease in shear strength of alloy depending on the H content in precipitates of second phase. We use the previously proposed multiscale approach combining molecular dynamics (MD), continuum modeling and discrete dislocation dynamics (DDD). H atoms are located inside precipitate and at interphase boundaries. Energetically preferable places of H accumulation near and inside θ' phase in Al-Cu alloy are revealed. It is shown that the H accumulation on θ' leads to a decrease in precipitate shear resistance and causes the change in the dislocation-precipitate interaction mechanism from the Orowan loop formation to the cutting of the inclusion. The H accumulation on precipitates causes an increase in the threshold stress for the dislocation nucleation on the inclusion. The mechanism of softening of inclusions associated with a change from looping to cutting is transferred to the DDD level. The DDD results demonstrate that H charging of Al-Cu alloy can substantially decrease its shear strength. For high strength alloys with small precipitate size and/or inter-precipitate distance and with the yield stress above about 460 MPa, the reduction of strength can reach 10–25%.