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Aluminum and aluminum alloy plating is difficult, because aluminum has a strong affinity for oxygen, the surface vulnerable to oxidation; aluminum is amphoteric metal in acid, alkali are unstable; aluminum potential is very negative, easily dip in the plating solution replacement of erosion and to be plated; aluminum expansion coefficient than most metals, therefore the coating easy to bubble, falling, impact strength.

Aluminum and aluminum alloy plating coating is the key to a special pre-treatment to remove the natural oxide film, and prevent its re-formation, and the aluminum piece immersed in electrolyte, to prevent displacement reaction. As a Navy aircraft overhaul facility, we often encountered in the repair process of aluminum and aluminum alloy plating. The experiment, and explore the optimal process conditions. Fu-plated aluminum alloy surface of the part not only good gloss and adhesion, corrosion resistance is also very good, to aids to navigation requirements. This article describes the old goods repair aluminum alloy plated parts blessing process.
A process
Degreasing (skim) → → stripping the old coating two alkaline etching → Cleaning → Cleaning → to two gray scaling (the light) → a sink two zinc → Cleaning → Cleaning → two zinc layer stripping → two cleaning → → zinc sulfate in the second sink and the activation of electroless nickel → Cleaning → Cleaning → → two picks → activation → plated two passivation → Cleaning → Cleaning → drying → two aging → inspector library.
2 shows the main process
2.1 degreasing solution composition and process conditions
Sodium hydroxide 40 a 609 / L, 70 a 90 "c, 1 a Zmin.
The first serious oil organic solvents to clean.
2.2 Stripping the old coating
Stripping the old tin alloy plating is one of the key processes.
2.2.1 Stripping the old welfare layer solution composition and operating conditions
Nitric acid left the money 10 for a 150 L, room temperature, and back to make up.
2.2.2 Zinc layer stripping the old solution composition and operating conditions
Sulfuric acid 10 to 150 left L, room temperature, and back to make up.
2.2.3 Stripping the old oxide film composition and operating conditions of sodium hydroxide solution, 40 a 609 / L, 50 a 90 "C, back to make up.
2.24 Ni-P alloy stripping solution composition and process conditions
Concentrated nitric acid 7 00mL / L, NaCl 30 to 409 / L, a hexamethylenetetramine 6 109 / L, urea 15, a ZoglL, room temperature.
(1) parts should be dried before stripping or drying with cold air to prevent people with reduced nitrate concentration in water, leading to corrosion of the substrate.
(2) stripping a good part should be promptly cleaned to avoid the surface layer after stripping the black oxide film.
Aluminum alloy commonly used electroless nickel deposits of concentrated nitric acid stripping. Although highly concentrated nitric acid oxidation, but the concentrated nitric acid on the Ni P alloy layer of a slow corrosion rate, when a large amount of stripping gas No second pollution to the environment greatly. Precision parts of a P alloy plating layer of Ni, after stripping, concentrated nitric acid corrosion on the amount of the base metal is often exceeded, especially for the bolt type parts have corrosion is particularly evident. In order to overcome Stripping electroless nickel layer on the bolt parts have corrosion of the shortcomings, we passed hundreds of tests, the final selection process out of the back of nickel. In addition to the withdrawal of a P Ni alloy layer, the corrosion of the substrate is very small and difficult to have corrosion, stripping of the gas is also less able to guarantee the quality of back-plated to improve the working environment.