Duplex Anodic Coating for Copper-Rich Aluminium Alloys
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Solution Overview
Problem
Current anodising processes for copper-rich aluminium alloys fail to provide optimal corrosion resistance and adhesion properties, with limitations in pore size and hydration sealing, and the use of chromate-based processes is restricted due to carcinogenic concerns.
Innovation Solution
A duplex anodising process involving a first anodising step in phosphoric acid followed by a second step in sulphuric acid, with a barrier layer thinning technique to reduce the forming voltage, allowing for a multi-layer anodic coating with large and small pore diameters for enhanced adhesion and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sulphuric acid anodising is used to achieve corrosion resistance through pore hydration sealing, then corrosion resistance is improved, but adhesion properties deteriorate due to pore closure
Solution Approach 1:
The patent divides the anodising process into two separate steps: first forming a phosphoric acid anodic layer with large pores for adhesion, then forming a sulphuric acid anodic layer with small pores for corrosion resistance. This segmentation allows each layer to fulfill its specific function without compromising the other.
Solution Approach 2:
The patent applies different acid treatments to different regions of the anodic coating structure. The phosphoric acid layer provides large-pore characteristics suitable for adhesion at the top layer, while the sulphuric acid layer provides small-pore characteristics for corrosion resistance at the bottom layer adjacent to the metal substrate.
2Strength
If phosphoric acid anodising is used to achieve excellent adhesion properties, then adhesion is improved, but corrosion resistance deteriorates due to inability to seal pores effectively
Solution Approach 1:
The patent separates the adhesion function and corrosion resistance function into two distinct anodic layers formed by different acid treatments, allowing each layer to optimize its specific function without compromise.
Solution Approach 2:
The patent creates a composite anodic structure combining phosphoric acid anodic oxide and sulphuric acid anodic oxide layers, where each material contributes its unique properties: phosphoric acid layer for adhesion and sulphuric acid layer for corrosion resistance.
3Reliability
If chromate-based anodising processes are used to achieve optimal corrosion resistance and adhesion, then performance is improved, but health safety deteriorates due to carcinogenic concerns
Solution Approach 1:
The patent replaces harmful chromate-based processes with a beneficial dual-acid anodising process using phosphoric and sulphuric acids, which achieves equivalent or superior performance without carcinogenic effects. This converts a harmful technology into a safe one while maintaining functionality.
Solution Approach 2:
The patent uses environmentally friendly phosphoric and sulphuric acid electrolytes instead of toxic chromate electrolytes, providing a sustainable and safe alternative that can be easily disposed of without hazardous waste concerns.
4Ease of manufacture
If a single-layer anodic coating is formed to simplify the process, then manufacturing complexity is reduced, but performance deteriorates due to inability to simultaneously optimize adhesion and corrosion resistance
Solution Approach 1:
The patent divides the coating into two functional layers with distinct properties, where each layer is optimized for its specific purpose. This segmentation enables simultaneous optimization of adhesion and corrosion resistance that cannot be achieved with a single-layer coating.
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 method achieves optimized corrosion resistance, adhesion, and abrasion properties, enabling full encapsulation of sol-gel materials while maintaining natural hydration properties, effectively replacing chromate-based technologies.
Implementation Method 1
an anodic coating comprising a porous layer of aluminium oxide being formed on the work piece through an electrochemical reaction in acidic electrolytes
Implementation Method 2
The oxide growth and nanopore formation mechanism is a result of flow of anodic alumina in the barrier layer region due to the combination of growth stresses and field assisted plasticity
Implementation Method 3
The stresses that drive the flow of material are due to electrostriction of the oxide layer which is plasticised under the electric field
Implementation Method 4
Hydration on the SAA surface proceeds rapidly after anodising and can be accelerated by hydrothermal treatment
Implementation Method 5
Hydration on the SAA surface proceeds rapidly after anodising and can be accelerated by hydrothermal treatment
Data Source
Figure 1~2(c)
Figure 3(a)~3(b)
Figure 4
AI summary
A method for producing a multi-layer anodic coating on a metal is described. The method comprises the steps of (i) placing the metal in a first electrolytic solution and applying a current to form a first anodic layer having a barrier region; (ii) reducing the applied current to cause a reduction in thickness of the barrier region; and (iii) placing the metal in a second electrolytic solution and applying a current to form a second anodic layer.