AlGa (Aluminum-Gallium) is a degenerate alloy that results from liquid gallium infiltrating the crystal structure of aluminium metal. The resulting alloy is very weak and brittle, being broken under the most minute pressure. The alloy is also chemically weaker, as the gallium inhibits the aluminum from forming a protective oxide layer. A video of gallium metal causing intergrain corrosion and breaking of aluminum can be found here.[1]
The alloy can be reacted with water to form hydrogen gas(H2), aluminum hydroxide and gallium metal.[2] Normally, aluminum does not react with water, since it quickly reacts in air to form a passivation layer of aluminum oxide. AlGa alloy is able to create aluminum nanoparticles for the hydrogen producing reaction.[3][4] Since this reaction forms hydrogen gas, it can be used as a source of fuel or simply as a hydrogen gas generator. This reaction can also be used to produce aluminum oxide from aluminum metal. As previously mentioned, aluminum normally won't react with water or air due to the presence of a protective passivation layer, but the reaction of suspended aluminum with water can effectively oxidize aluminum to form aluminum hydroxide which can then be heated to about 180 °C (356 °F), where it decomposes to produce aluminum oxide and water vapor.
Due to AlGa's extreme lack of structural integrity and inability to form a protective oxide layer, gallium metal is considered to be corrosive. If AlGa were to form on an aluminum structure, the aforementioned structure could weaken or collapse. Gallium is illegal to transport on aircraft as it could compromise the integrity of the aluminum hull.