I have a customer who wants to paint some magnesium parts. Some people have told me that magnesium may be difficult to paint. Can you provide any information on pretreatment, primer and paints that are commonly used? P. S.
Magnesium is really not too difficult to paint. Degreasing, pretreated by deoxidizing and priming prior to painting, cleans it. Since magnesium is more alkali resistant than aluminum, it is degreased using strong alkaline cleaners. Deoxidizing can be done by acid pickling with chromic acid. Blast cleaning will also remove oxidation. However it must be done carefully so that oily residues and corrosion-causing contaminants are not driven into the magnesium surface. Surfaces should always be degreased before blast cleaning.
I will only provide a list of chemical pretreatments for magnesium, because the details of these pretreatments are beyond the scope of the Painting Clinic. More detailed information can be attained from pretreatment chemical suppliers (www.pfonline.com/suppliers.html). The pretreatments for magnesium are: Type I Chrome-Pickle treatment, Type II Sealed Chrome-Pickle treatment, Type III Dichromate treatment, Type IV Galvanic Anodizing treatment, the HAE process, Acid Chromate Anodic process. Many of these pretreatments involve multiple stages, which is probably the reason people say magnesium may be difficult to paint. You may want to consider outsourcing the pretreatment to a custom coater or electroplating shop. Primers for magnesium generally contain zinc chromate pigment. Certain zinc chromate primers are actually pretreatments and should be applied directly to bare, cleaned magnesium and not be applied over other pretreatments. After priming, most paint finish systems can be used for painting magnesium.