Metallurgical Features of Plasma Surfacing Repair of Magnesium Alloys

Results are provided for studying formation of the structure and properties of products made of high-strength light alloy ML5 of the magnesium-aluminum-manganese-zinc system using plasma surfacing with a reverse polarity current in repair technology. These studies show that plasma surfacing with a reverse polarity current provides high quality repair of casting defects for magnesium alloys of the ML5 type. Correct selection of plasma surfacing parameters ensures total absence of incomplete melting and cracks within deposited material. It is established that plasma surfacing over a wide range of regime changes provides dispersion of deposited metal structure by an order of magnitude greater than for structures of the ML5 base initial cast metal regardless of its condition (heat treatment); heating surfacing regimes provide an additional increase in fine-grained deposited metal hardness. As a result of a cathodic cleaning effect an oxidized layer on a magnesium alloy surface is completely removed and there is no deposited metal contamination with dissociation products. This confirms the effectiveness of using plasma surfacing with a reverse-polarity arc to restore ML5 products that have undergone chemical and heat treatment, and at the same time eliminating a time-consuming operation of oxidized coating removal. Plasma surfacing with a reverse polarity current provides deposited metal with a good set of mechanical properties: a unique 5–9-fold increase in ductility compared to cast material with an increase in strength properties by 7–10%, both with and without heat treatment.