The interaction of Mg and Al2O3 during diffusion bonding of aluminum 6061 plates are studied using thermochemical simulation software to understand how reactions between Mg and Al2O3 may change with temperature and system pressure parameters. The results show that reactions between Mg and Al2O3 to produce either MgO + Al or MgAl2O4 + Al are thermodynamically favorable and serve to reduce the Al2O3 so that Al/Al metallic bonds can form. Calculations to determine the equilibrium partial pressure of oxygen show that the partial pressure of oxygen is larger at higher temperatures. For example, the partial pressure of oxygen at the phase boundary between Al(s)+Mg2Si(s)+Si(s) and Al(s)+MgO(s) +Si(s) increases from Log10(pO2) -= -75.6 atm to -65.1 when the temperature increases from 723 K to 823 K. Calculations also show that increases in system pressure have no impact on the reduction reaction, the reaction products, or the calculated partial pressure of oxygen at the phase boundaries. Calculations were performed with Si added to the system and it is shown that Mg2Si only forms at low oxygen partial pressure values, and that no impacts of system pressure occur. From this work we can conclude that the temperature plays an important role in determining the partial pressure of oxygen attained in the reduction reaction and in controlling the reaction products and that pressure has no role in affecting the reaction or its products. For example, at 723 K all of the initial Al2O3 is consumed when the partial pressure reaches Log10(pO2) = -69.8 atm while at 823 K it is consumed at Log10(pO2) = -60.0 atm.
