Corrosion of aluminium and magnesium alloys

1、Corrosion in various media

In most organic acids, inorganic acids and neutral media solution, magnesium aluminum alloy corrosion resistance performance is poor, and when the removal of magnesium aluminum alloy surface oxide film, even distilled water will lead to the corrosion of magnesium aluminum alloy speed up. But when the magnesium aluminium alloy is in chromic acid solution, its surface will form a certain passivation film, so that it has better stability and corrosion resistance. If it is easy to contain Cl- and SO42-, the corrosion of the surface of magnesium aluminium alloy will be accelerated, while if it is in the solution containing SiO32-, CrO42-, Cr2O72- plasma, the surface of magnesium aluminium alloy will be chemically reacted with oxygen atoms in various ions to form an oxide film on its surface, thus having a high corrosion resistance.

2、Electro-couple corrosion and total corrosion

As the electrode potential of magnesium aluminium alloy is lower than that of most metals, therefore, once the magnesium aluminium alloy and these metals are in contact with each other, it will occur when the electric couple corrosion. For Fe, Ni, Cu and other metals with low hydrogen over potential, if as impurities exist in the content of magnesium aluminium alloy, it will constitute a corrosion for battery with magnesium, resulting in serious galvanic corrosion of magnesium aluminium alloy. For Zn, Cd and other metals with high hydrogen overpotential, the galvanic coupling corrosion suffered by magnesium aluminium alloy is not obvious.

3, pitting corrosion and filiform corrosion

Magnesium aluminium alloy if exposed to non-oxidizing media containing Cl-, pitting corrosion will occur, in neutral or alkaline solution, magnesium aluminium alloy surface pitting corrosion will further intensify. If the magnesium aluminium alloy is immersed in NaCl solution, after a certain induction, the surface of magnesium aluminium alloy will appear pitting corrosion phenomenon.