ASTM F1428 Organic Aluminium Particle Filled Basecoat with Organic/inorganic TopCoat Coating for Fasteners
ASTM F1428 specification covers the basic requirements for a corrosion-resistant coating consisting of an inorganic aluminum particle-filled basecoat and an organic or inorganic topcoat, depending on the specific requirements.
The coating may be specified with basecoat only, or with the top coated with compatible organic polymer or inorganic topcoats, depending on the specific requirements. The basecoat is a water-dilutable slurry containing aluminum particles dispersed in a liquid binder of chromate/phosphate compounds. The organic topcoats consist of polymer resins and dispersed pigments and are for service where temperatures do not exceed 230°C (450°F). The inorganic topcoats consist of ceramic oxide pigments dispersed in a liquid binder of chromate/phosphate compounds and are for service where temperatures do not exceed 645°C (1200°F). These coatings are applied by conventional dip/spin, dip/drain, or spray methods. The coating process does not normally induce hydrogen embrittlement, provided that the parts to be coated have not been subjected to an acid cleaner or pretreatment
- The coatings shall have a smooth, uniform appearance and shall be free of lacerations and other discontinuities that may affect the appearance or performance of the coatings. All topcoat colors shall be agreed upon by both the purchaser and the supplier.
- The coating shall show no evidence of blistering or other appearance changes after exposure to humidity testing for 96 h, it shall show no more than 3.0-mm peel-back from the intersection of scribed lines that are tape-tested immediately after a 10-min
recovery period from the humidity test, and there shall be no other peeling under the tape.
- These coatings shall be capable of withstanding neutral salt spray testing for the minimum time specified in Table above. Unless otherwise defined, acceptable corrosion resistance shall be considered to be met where there is no base metal corrosion
on signifiant surfaces.
Significant surfaces on threaded fasteners are defined as the surfaces exposed when the fasteners are installed in a normal manner (bolt head, nut drive, face, and so forth). On other surfaces on which coating control cannot be obtained under
normal processing, such as holes, recesses, threads, and so forth, the above requirements do not apply.
- The coating shall not have an adverse effect on normal installation and removal practices, as determined by the proper “GO” thread gage or the fit and function inspection method .
- The thickness of the coating is limited by the basic thread size. Where greater thickness is necessary, threads may be produced undersize or oversize (before coating) to accommodate the coating thickness, providing that the finished fastener (after
coating) meets all specified mechanical properties, as agreed upon by the supplier and the purchaser.
- The coatings shall show no blistering, peeling, cracking, loss of adhesion, discoloration, or red rust on significant surfaces after exposure to the weathering test for at least as many hours as specified for salt spray resistance for the various
- Any conventional cleaning procedure that does not induce hydrogen embrittlement or intergranular attack of the basis metal can be used, followed by grit blasting or micro-zinc phosphating . If not properly controlled, zinc phosphate coatings and
certain acid descaling processes may produce hydrogen embrittlement or severe etching of the basis metal.
- The coatings are applied by conventional dip/spin, dip/drain, or spray methods.
- The coatings shall be applied under suitable control conditions and in the stages necessary to meet the requirements of the specification. Unless otherwise specified, these coatings shall be applied after all machining, forming, and heat treatments
have been completed, but prior to final inspection.
- The contractor (applicator) shall maintain control over factors that affect the quality of the treatment, including, but not limited to, dip/spin parameters, coating viscosities, and temperature. Chemical analyses, coating replenishment, visual
inspection, and other process control devices shall be conducted with the frequency required to maintain good quality of the treatment and to meet the requirements of ASTM F1428 specification. Visual inspection is intended to include appearance
factors such as (1) streaking, (2) dulling, (3) uncoated areas, and (4) loss of color where color is specified.
- Corrosion resistance shall be tested in accordance with Practice B117.
- Coating Thickness
- Coating thickness shall be tested in accordance with Test Methods D1186, magnetic-permeability; Practice E376, eddy-current; or Test Method B568, X-ray spectrometry. For referee purposes, micro-examination in accordance with Test Method B487 shall
- Humidity Test
- The humidity test shall be conducted in accordance with Practice D2247.
- After exposure to the humidity test, adhesion shall be tested in accordance with Test Methods D3359.