Optimization of mechanical properties in aluminum alloys via hydrogen partitioning control

Synopsis: This review reports the research activity on the hydrogen embrittlement in high-strength aluminum alloys, especially focusing on hydrogen trapping at various trap sites and its influence on hydrogen embrittlement. We have investigated the three representative hydrogen embrittlement mechanisms in high-zinc-concentration Al-Zn-Mg alloys. One of the three mechanisms is the damage evolution originated from hydrogen precipitated as pores. We have paid marked attention to the existence of age-hardening precipitates as the major hydrogen trap site. Firstly, we have clarified the nanoscopic structures of a few MgZn ₂ precipitates and their interface by means of the high-resolution TEM technique. Such information has been utilized to perform a first principles simulation to know trap binding energy values for almost all the possible trap sites. At the same time, detailed fracture micromechanisms and microstructure-property relationships have been investigated by employing both the high resolution X-ray micro-tomography technique and the first principles simulation. The ultra-high-resolution X-ray microscope, which has been realized quite recently, has also been applied. Characteristic localized deformation and subsequent crack initiation and growth through deformed aluminum have been observed. It has also been revealed that hydrogen embrittlement has been suppressed when relatively coarse particles are dispersed. In-situ hydrogen repartitioning during deformation and fracture has been estimated by considering thermal equilibrium among the various trap sites together with the increase in trap site density during deformation. The relationship between the in-situ repartitioning of hydrogen and hydrogen embrittlement with the three different micromechanisms are discussed to explain realistic conditions for hydrogen embrittlement to occur.