Mg-Li Alloy Surface Layer for Corrosion Resistance
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Solution Overview
Problem
Magnesium-lithium alloys (Mg—Li alloys) suffer from inadequate corrosion resistance due to the high reactivity of lithium, leading to increased corrosion rates, especially when compared to magnesium alloys without lithium, and existing surface treatment methods only improve corrosion resistance in the surface layer without addressing the underlying material issues.
Innovation Solution
A Mg—Li alloy with a high degree of orientation in the (110) plane of the β-phase and an average grain size of less than 50 micrometers, combined with a surface layer formed through anodization, where the lithium concentration is lower than the interior, creating a protective anticorrosive film composed mainly of magnesium fluoride.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If lithium is added to magnesium alloy to reduce density and improve specific strength, then weight reduction and specific strength are improved, but corrosion resistance deteriorates due to high reactivity of lithium
Solution Approach 1:
The patent applies local quality by creating a surface layer with different lithium concentration than the interior. The surface layer has lower lithium concentration (higher magnesium concentration) to provide corrosion resistance, while the interior maintains high lithium concentration for lightweight properties. This is achieved through selective surface treatment that modifies only the surface composition without changing the bulk alloy properties.
Solution Approach 2:
The patent segments the alloy structure into two distinct regions: a surface layer and an interior region. The surface layer is treated separately to have different chemical composition (lower Li, higher Mg) compared to the interior (higher Li). This segmentation allows each region to optimize its function - surface for corrosion resistance, interior for lightweight structural properties.
2Reliability
If surface treatment is applied to reduce lithium concentration at the surface, then corrosion resistance is improved, but the treatment is only effective for surface layer and insufficient for overall member
Solution Approach 1:
The patent changes the lithium concentration parameter selectively in the surface layer compared to the interior. By controlling the lithium concentration gradient (lower at surface, higher in interior), the patent achieves both corrosion resistance at the surface and maintains the lightweight properties in the bulk. This parameter change approach allows simultaneous optimization of contradictory properties at different locations.
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
This approach significantly enhances the corrosion resistance of the alloy member by reducing lithium concentration on the surface, preventing corrosion and improving durability, making it more resistant to environmental exposure.
Implementation Method 1
forming a surface layer on the base material by performing an anodization process on the base material to obtain the surface layer having a Li concentration lower than a Li concentration of inside of the base material
Implementation Method 2
performing an anodization process on the base material
Implementation Method 3
an anticorrosive film is able to be formed on the surface layer
Data Source
AI summary
An alloy member includes a base material that includes a surface layer and is a magnesium-lithium alloy (Mg—Li alloy) having an α-phase and a β-phase, and an anticorrosive film is able to be formed on the surface layer. A degree of orientation in a (110) plane of the β-phase of the Mg—Li alloy is more than or equal to 70%. An average grain size of the Mg—Li alloy is less than or equal to 50 μm. A Li concentration of the surface layer is lower than a Li concentration of inside of the base material.