Al-Cu合金鋳物中の水素拡散係数

抄録

Hydrogen diffusivity D(m²s^-1) in the ingot of Al-(0-50mass%)Cu alloys were measured for ND-samples solidified unidirectionally in pure nitrogen gas fllow. The Arrhenius type dependence of D on temperature is realized above about 400°C, but an upward departure is noted below 400°C. In the region of α-solid solution (Cu<5.7mass%), D decreases with the addition of copper. In the coexistent region of primary and eutectic crystals (5.7<Cu mass%<52.6), D is controlled by the following two factors, (1) an enhanced diffusion of hydrogen along the interface between primary and/or eutectic crystals and (2) a suppressed diffusion by hydrogen trapping at eutectic-lamellae interfaces. The value of D for θ-phase is a little greater than that for α-solid solution with 5.7mass%Cu. For AM samples melted in air, D is clearly smaller than that of ND or VM samples melted in vacuum with no voids. The Arrhenius type plots D=D₀exp (-Q/RT) above 400°C have yielded a linear relationship between log D₀(m²s^-1) and Q(kJ•mol^-1), namely D₀=2.22×10^-8 exp (0.138Q).