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Fuel cells are often seen as a long-term solution to environmental problems such as CO 2 emission associated with transportation. To ensure long-term sustainability and the supply of fuel, new renewable of hydrogen (H 2 ) generator have to be introduced. In this study, Ni-rich AZ91D magnesium alloy ingot, which was considered as waste material, was used as a H 2 generator in sodium chloride (NaCl) solution with catalyst. The chemical reaction Mg þ H 2 O ! H 2 þ Mg(OH) 2 occurred in NaCl aqueous solution. The H 2 evolution rate depended on the solution's temperature (25 or 70 C), length of catalyst (0.9 or 1.8 m) and the concentration of NaCl solution (5 or 10 mass%). The H 2 evolution rate increased with increasing the solution's temperature. The catalyst (Pt wire) could significantly improve the H 2 generation rate. In addition, the by-product of this method is Mg(OH) 2 , a non-toxic chemical compound which is usually used as flame retardant.

Mg 17 Al 12 compound is a hardening phase in AZ91D alloy. Moreover, the concentration of Al and Zn has been found to be closely related to the corrosion performance of the magnesium alloy. The aim of this work was to study the effect of cooling rate on distribution of Mg 17 Al 12 compound and compositional inhomogeneity in an AZ91D magnesium sand-cast plate (200 Â 140 Â 20 mm 3 ). A copper chill block, which was placed at the end of mold cavity, was used to increase the cooling rate during solidification. A sand-cast plate was also produced, where no chill block being mounted at the end of mold cavity. The ''with chill block'' plate showed a rapid increasing in cooling rate with respect to distance from riser, as compared to the ''without chill block'' plate where almost no cooling rate fluctuation occurred. The volume fraction of Mg 17 Al 12 ( phase) in the ''without chill block'' plate was higher than that in ''with chill block'' plate. In the ''without chill block'' plate, volume fraction of Mg 17 Al 12 was about 13.9 vol% (near the riser) to about 19.3 vol% (close to the end of the plate). However, the ''with chill block'' plate was solidified in a higher cooling rate, leading to low volume fraction of the phase (13.4 vol%). Higher cooling rate also resulted in more severe compositional inhomogeneity in the sand-cast plate. The Al and Zn concentration in the ''with chill block'' plate showed a concave downward dependence against the distance to riser. Moreover, in the ''with chill block'' plate, concentrations of Al and Zn did not enrich at the position near chill face. Instead, the Al and Zn contents near the chill surface were well below the average value. This finding is in disagreement with previous studies.

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