The Effect of Laser Surface Modification on the Corrosion Behaviour of Iron and Aluminum Base Alloys

The effect of laser surface modification on the corrosion behaviour of Fe--10Cr--13P--7C and Al--Si base alloys was studied. Using the laser powder injection technique an amorphous surface layer with a composition Fe--10Cr--13P--7C could not be obtained, although this alloy is amorphous after melt-spinning. Formation of crystalline phases in the system Fe--Cr--P--C led to a high compositional heterogeneity due to the low solubility of phosphorus and carbon in the iron matrix. This resulted in a low corrosion resistance and a selective dissolution of phases with a low chromium and phosphorus content. The pitting corrosion resistance of aluminium alloys could be significantly improved by laser surface remelting. The positive effect of the laser remelting became less significant for alloys containing high amounts of silicon and not observed in the presence of primary silicon particles. A common feature for both material groups was the non-uniform attack on the laser-treated samples. Especially typical was the selective dissolution of the interface regions of the neighboring laser traces. The results showed clearly that the formation of a homogeneous structure comprising both the central part of the laser traces and the interfacial regions would be required in order to achieve laser-treated surface layers with a high corrosion resistance.