Abstract
This specification covers the chemical and anodic treatments used to prepare magnesium alloy surfaces for printing. The procedures for preliminary surface treatment using alkaline and acidic cleaners are described. Class I Type I (chrome pickle) surface treatment procedure is applicable to all forms of magnesium, except for certain special alloys containing silver. I class II (seal cr kimchi) surface treatment procedures are applicable to all types and forms of magnesium alloy, only restricted by the I class I class to handle. Type I and type III processing are applicable to all types and forms of magnesium alloy, but the M1 alloy and some similar to EK30A except for rare earth alloy. Class II Type I (electroplated dichromate treatment) produces a black coating with good protective and analgesic qualities for all alloys and forms of magnesium, including the M1 alloy. Class II, Type II treatment is applicable to all forms and alloys of magnesium. Class II, Type III treatment is applicable to all forms and alloys of magnesium without attachments or inserts of other metals.

ASTM D1732-2018 “Surface Treatment of Magnesium Alloys for Painting”

The concept
1.1 These practices cover two classes of treatments used to prepare magnesium alloy surfaces for coating, as follows:

The first category – chemical treatment.

The second category – anodic treatment.

In general, the latter treatment is more protective in both categories. Mechanical (abrasive) treatment, solvent cleaning, alkaline solution treatment, and acid pickle do not result in protective conversion coatings are preliminary treatments suitable for metals exposed only under mild corrosive (indoor) exposure. When you need a high degree of corrosion protection and paint adhesion, such as in many outdoor environment, surface treatment using conversion coating is one of the categories above. The use of a method based on hexavalent chromium is not recommended because hexavalent chromium is a known carcinogen.

Note 1: Coating tests – Quality control tests for coatings are usually desirable. These tests usually include exposure to salt spray, humidity or the natural environment, with or without paint, and have procedures in place to assess the degree of breakdown suffered after fixed time intervals. Coating quality control testing is recommended to use high-purity materials such as AZ31A alloy whenever possible, 2 whose inherent corrosion rate varies from batch to batch, and precautions should be taken to remove surface contaminants prior to coating application. Such contaminants should be removed by pickling to a depth of at least 0.001 inches (25 micmeters) on each side.

ASTM D1732-2018 “Surface Treatment of Magnesium Alloys for Painting”

1.2 this standard may involve hazardous materials, operations, and equipment. This standard is not intended to address all safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health and environmental practices and to determine the applicability of regulatory restrictions prior to use. See note 11.

1.3 This international Standard has been developed in accordance with the internationally recognized standardization principles established in the Decision on Principles for the Development of International Standards, Guidelines and Recommendations issued by the Committee on Technical Barriers to Trade of the World Trade Organization.