Aluminum Alloy Piston Coating Surface Roughness Control
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Solution Overview
Problem
The existing electrolytic oxidation ceramic coatings on pistons tend to develop large surface projections, leading to increased abrasion and aggressiveness towards mating members due to high surface roughness and hardness, particularly when silicon is present in the aluminum alloy base material.
Innovation Solution
A method for forming an electrolytic oxidation ceramic coating with a surface roughness of Ra ≤ 0.7 µm and average hardness ≤ HV 600, involving an electrolyte with a molar ratio of zirconium to titanium between 1:0.5 to 1.5, using alternating current voltage with a duty ratio of 0.1 to 0.8, and applying both positive and negative electric potentials with non-energization times to restrict surface projection generation and enhance coating smoothness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If electrolytic oxidation ceramic coating is formed with high hardness (HV 800 or more) to improve abrasion resistance, then the coating provides prominent abrasion resistance and high strength, but large surface projections are generated leading to increased surface roughness and higher aggressiveness to mating members
Solution Approach 1:
The invention changes the chemical composition parameters of the electrolyte by adding specific compounds (boric acid, sodium fluorosulfonate, and titanium compounds) to control the coating formation process. This results in a coating with optimized hardness (HV 600-800) that balances abrasion resistance with reduced surface roughness (Ra ≤ 0.7 μm), preventing excessive surface projections while maintaining protective properties
Solution Approach 2:
The invention creates a composite coating structure containing multiple oxide phases (alumina, zirconium oxide, and titanium oxide) formed through electrolytic oxidation. The titanium oxide component specifically contributes to smoothing the surface and reducing projections, while the composite structure maintains high hardness and abrasion resistance
2Manufacturing precision
If alternating current voltage with duty ratio 0.1 to 0.8 is used to control surface projection generation, then surface roughness is reduced to Ra ≤ 0.7 μm, but the coating formation process becomes more complex
Solution Approach 1:
The invention employs alternating current voltage with a duty ratio of 0.1 to 0.8, creating periodic energization and non-energization cycles during electrolytic oxidation. This periodic action controls the formation and removal of surface projections, achieving smooth surfaces (Ra ≤ 0.7 μm) by preventing excessive coating buildup while maintaining protective hardness properties
Data Source
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AI summary
An aluminum alloy member includes a main body (1) including an aluminum alloy serving as a base material, and an electrolytic oxidation ceramic coating coated at a portion of a surface of the main body (1) and including a most outer layer and an inner layer which is arranged close to the main body (1) relative to the most outer layer, the inner layer in which an aluminum oxide is richer than the most outer layer, the most outer layer in which a volume of a titanium oxide or a total volume of the titanium oxide and a zirconium oxide is richer than the inner surface.