ASTM D1732-03 (R2018) pdf free download.Standard Practices for Preparation of Magnesium Alloy Surfaces for Painting.
1.1 These practices cover two classes of treatment for preparation of magnesium alloy surfaces for painting, as
follows:
Class I—Chemical Treatments.
Class II—Anodic Treatments.
In general, the latter treatments are the more protective of the two classes, Mechanical (abrasive) treatments, solvent cleaning, alkaline solution treatments, and acid pickles not resulting in protective conversion coatings are suitable preliminary treatments only for metal to be exposed under mildly corrosive (indoor) exposures. When a high degree of corrosion protection and paint adhesion are desired, as in many outdoor environments, surface preparation by one of the above conversion-coat classes is necessary. The hexavalent chromium based methods given are not recommended as hexavalent chromium is a known carcinogen.
Note 1—Testing of Coatings—Qualily control tests of coatings are frequently desirable, and these generally Consist of exposures, with or without paint. to salt spray. humidity, or natural environments, with suitable procedures for assessing the dcgree of breakdown suffered after tixed time inervals. It is recommended that quality control teSts 01 coatings shall be made as far as possible with high-purity material (for example AZ3IA alloy).2 the inherent corn)sion rate of which is relatively consistent from hatch to hatch and that precautions shall be taken to remove surface contaminalion before coatings are applied. Such contamination shall be removed by acid pickling to a depth of at least 0.001 in. (25 pm) per side.
2. Procedure
2. 1 Certain anodic treatments simultaneously produce conversion coatings on, and remove contamination from, niagneslum alloy surfaces. In general, however, apply conversion coatings only to surfaces previously freed from all contamination. including oxide, rolling-scale. corrosion product, burned—on drawing and forming lubricant, and the contamination introduced by blast cleaning and fabrication operations. Contamination in or under surface conversion coatings senously reduces their protective values (Note 2). For the removal of tenacious surface contamination, such as rolling-scale or casting skin, an acid pickle to dissolve some of the actual surface is essential. When organic contamination, such as grease or oil, is also present, an initial degreasing operation iii solvent or in an alkaline degreasing solution is usually necessary to allow the subsequent acid to wet the surface. These matters are discussed in more detail under the headings of the specific cleaners or treatments (Note 3). as follows:
2.2 Alkaline Cleaners—Oil, grease, and old (but not baked) chrome-pickle coatings are readily removed by most commercially available heavy-duty alkaline cleaners: hut such cleaners are not suitable for removing oxide and the like, for which purpose use acid pickles. preceded by alkaline cleaners. Remove graphite lubricant and also baked chronic-pickle coatings by a solution conforming to the following compostion.ASTM D1732 pdf download.