Magnesium-Lithium Alloy Coating with High Fluorine Content
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Solution Overview
Problem
Conventional magnesium-lithium alloys have insufficient corrosion resistance due to the inability to form a coating film with a large amount of fluorine, leading to poor performance in high-temperature and high-humidity environments.
Innovation Solution
A magnesium-lithium alloy substrate with a coating film containing more than 50 atom % fluorine and less than 5 atom % oxygen is developed, formed through an anodization process using a neutral ammonium fluoride solution, which suppresses hydrogen gas generation and enhances corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fluorination methods (dip treatment with acidic ammonium fluoride or conversion treatment with hydrogen fluoride) are used on magnesium-lithium alloy, then the surface is treated to improve corrosion resistance, but the fluorine content in the coating film remains insufficient (less than 50 atom %)
Solution Approach 1:
The patent changes the chemical parameters of the treatment liquid from acidic to neutral pH, and adjusts the composition to contain ammonium fluoride and aluminum in specific proportions. This parameter change enables the formation of a coating film with fluorine content exceeding 50 atom %, resolving the contradiction between achieving high fluorine content and maintaining effective corrosion protection.
Solution Approach 2:
The patent creates a composite coating film containing multiple elements (fluorine, aluminum, magnesium, lithium) with specific compositional ratios. This composite structure, formed through electrochemical conversion in neutral ammonium fluoride solution, achieves both high fluorine content (>50 atom %) and excellent corrosion resistance by synergistically combining the protective properties of fluorinated compounds with aluminum-containing phases.
2Weight of moving object
If magnesium-lithium alloy is used to achieve light weight, then weight reduction is accomplished, but corrosion resistance deteriorates in high-temperature and high-humidity environments
Solution Approach 1:
The patent applies a preliminary conversion treatment to the magnesium-lithium alloy surface before the alloy is exposed to corrosive environments. This pre-treatment forms a protective coating film containing fluorine and aluminum, which acts as a barrier against corrosion. The treatment is performed in advance using neutral ammonium fluoride solution, preventing corrosion before it can occur in high-temperature and high-humidity conditions.
Solution Approach 2:
The patent changes the pH parameter of the treatment liquid from acidic to neutral, which fundamentally alters the corrosion behavior and coating formation mechanism. This parameter change enables the formation of a stable, protective coating on magnesium-lithium alloy that maintains integrity in high-temperature and high-humidity environments, thereby improving reliability without sacrificing the lightweight advantage.
3Ease of manufacture
If dip treatment with acidic ammonium fluoride is applied to magnesium-lithium alloy, then surface treatment is performed, but the coating film cannot contain a large amount of fluorine
Solution Approach 1:
The patent inverts the conventional approach by using neutral pH instead of acidic pH for the ammonium fluoride treatment. This inversion of the pH parameter fundamentally changes the electrochemical environment, enabling the formation of a coating film with high fluorine content (>50 atom %) while maintaining process simplicity and ease of manufacture.
Solution Approach 2:
The patent changes the pH parameter from acidic to neutral, and adjusts the composition parameters (ammonium fluoride concentration, aluminum content) to achieve optimal coating formation. These parameter changes enable the coating film to incorporate large amounts of fluorine (>50 atom %) while keeping the manufacturing process simple and efficient.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The resulting alloy member exhibits improved corrosion resistance and reduced hydrogen gas generation, even when exposed to severe environments, with a fluorine-rich coating film thickness of 25 μm or more, effectively inhibiting corrosion.
Implementation Method 1
disposing a cathode substrate and the substrate made of magnesium-lithium alloy as an anode in an aqueous solution of neutral ammonium fluoride; and applying a voltage between the anode and the cathode to dispose a coating film on the substrates
Implementation Method 2
applying a voltage between the anode and the cathode to dispose a coating film on the substrates
Data Source
AI summary
Provided is an alloy member including a substrate made of magnesium-lithium alloy with a sum of content of magnesium and content of lithium of 90 mass % or more and a coating film disposed on the substrate. The coating film contains fluorine and oxygen, with a fluorine content of more than 50 atom % and an oxygen content of less than 5 atom %.