The effect of Cu or Ni addition on creep properties of a heat-resistant aluminum (Al) alloy (with a composition of Al-5Mg-3.5Zn (mol%)) strengthened by precipitates of T-Al₆Mg₁₁Zn₁₁ intermetallic phase was investigated. The quaternary alloys with various Cu contents (0.25-3 mol%) or Ni contents (0.5-2 mol%) were solution-treated at 470°C and then aged at 200°C for 10 hours. The creep tests were conducted using the heat-treated specimens at 200°C under 105 MPa. Both Cu and Ni additions increased the creep rupture time. The 1 mol% Cu added alloy exhibited the longest creep rupture time due to the enhanced precipitation of the refined intragranular phases (T or MgZn₂ phases). However, more than 2 mol% Cu addition led to the transition of T phase to S-Al₂CuMg phase formed on grain boundaries. The phase transition might have a detrimental effect on creep rupture time. In the Ni-added alloy specimen, the creep rupture time became longest when 1 mol% Ni was added. The added Ni element promoted the formation of the Al₃Ni phase on the grain boundaries, resulting in the suppression of connecting cavities formed on grain boundaries in creep deformation.

In this study, hydrogen incorporated into 7075 aluminum alloy substrates by electroless Ni-P plating was investigated. In the cross-sectional transmission electron microscope images, a low phosphorus content (5.7mass%) film consisted of fine grains and a high phosphorus content (12.1mass%) film consisted of an amorphous phase were observed on the 7075 alloy substrates. Depth profile analysis by glow discharge optical emission spectrometry revealed that the intensity of hydrogen increased in the 7075 alloy substrate after electroless Ni-P plating, and was higher at the interface between the Ni-P film and the 7075 alloy substrate. In the thermal desorption spectra of hydrogen from the 7075 alloy substrates with low and high phosphorous content Ni-P films, a pronounced desorption peak and a series of desorption peaks were observed. Such desorption peaks were not observed in the 7075 alloy substrate before electroless Ni-P plating and in the Ni-P films on the copper substrates. These results indicate that the hydrogen incorporated into the 7075 alloy substrate by electroless Ni-P plating exists in various trap sites such as interstitial sites, vacancies, grain boundaries, and the incoherent interface between the precipitates and the aluminum basal phase.