Clad Material for Automotive Cooler Corrosion Resistance
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Solution Overview
Problem
Conventional coolers for electric and hybrid automobiles face challenges in achieving both high corrosion resistance and efficient cooling performance due to the susceptibility of thin top sheets to corrosion, especially when exposed to cooling water, which leads to rapid corrosion pitting and inadequate joint strength.
Innovation Solution
A clad material with a three-layer structure, comprising a core material and two brazing filler metal layers, is developed, where the finish rolling ratio is specified between 10 to 25%, enhancing press formability, brazing capability, and corrosion resistance by controlling recrystallization and providing a sacrificial anode effect to inhibit corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the top sheet is thinned down to improve cooling efficiency, then heat exchange efficiency is improved, but corrosion resistance deteriorates and corrosion pitting occurs rapidly
Solution Approach 1:
The invention uses a clad material comprising a core material (aluminum alloy sheet) and a cladding material (aluminum alloy with different composition) bonded together. The core material provides structural integrity and press formability, while the cladding material provides superior corrosion resistance. This composite structure allows the top sheet to be thin for efficient cooling while maintaining corrosion resistance through the protective cladding layer.
Solution Approach 2:
The invention applies different material properties to different parts of the top sheet by using cladding. The cladding material is applied specifically to the surface that contacts cooling water, providing localized corrosion protection where it is most needed, while the core material maintains the overall structural requirements.
2Ease of manufacture
If conventional aluminum alloy materials are used for the top sheet, then press formability is maintained, but corrosion resistance cannot be improved
Solution Approach 1:
The clad material combines a core material optimized for press formability with a cladding material optimized for corrosion resistance. The core material can be conventional aluminum alloys that are easy to form, while the cladding layer provides the necessary corrosion protection, allowing both requirements to be satisfied simultaneously.
Solution Approach 2:
The invention changes the material composition parameters by using a clad structure with different aluminum alloy compositions in the core and cladding. This allows optimization of different parameters (formability from core, corrosion resistance from cladding) that cannot be simultaneously optimized in a single homogeneous material.
3Strength
If brazing is performed to join cooler components, then structural integrity is improved, but erosion occurs due to molten brazing filler metal penetrating into subgrain boundaries
Solution Approach 1:
The cladding material serves as a protective barrier during brazing, preventing molten brazing filler metal from penetrating into the core material's subgrain boundaries. The cladding layer absorbs or redirects the brazing filler metal, eliminating erosion while maintaining strong joints.
Solution Approach 2:
The cladding material acts as an intermediary layer between the core material and the brazing filler metal. It mediates the interaction during brazing, preventing direct contact between the brazing filler metal and the core material, thereby preventing erosion while still allowing strong joint formation.
4Reliability
If cooling water flow is increased to improve cooling performance, then heat exchange efficiency is improved, but corrosion pitting occurs more rapidly
Solution Approach 1:
The clad material with its corrosion-resistant cladding layer allows the use of high-velocity cooling water flow for improved cooling performance without suffering from accelerated corrosion pitting. The cladding layer protects the underlying core material from the corrosive effects of high-velocity water flow.
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 clad material allows for precise press forming, reliable brazing, and effective corrosion resistance, preventing corrosion pitting even under high-velocity cooling water flow, thereby enhancing cooling performance.
Implementation Method 1
the core material undergoes recrystallization in the heating process associated with brazing during the production of a cooler that uses a clad material
Implementation Method 2
the molten brazing filler metal then preferentially penetrates into the subgrain boundaries and so-called erosion occurs
Implementation Method 3
the clad material for a cooler has an excellent corrosion resistance when used as a top sheet and thus inhibits the occurrence of corrosion pitting
Data Source
Figure 1~2
AI summary
A clad material (20) for a cooler is provided by executing production of a tensile strain of 3 to 10% or rolling at a finish rolling ratio of 10 to 25%, and optionally performing a heat treatment for 1 to 8 hours at a temperature within a range from 150 to 400°C, on a clad raw material having a three layer structure of a core material (21), a first brazing filler metal layer (22) that covers one side (the surface on the side of a cooling water passage (4)) of this core material (21), and a second brazing filler metal layer that covers the other side (the surface on the opposite side from the cooling water passage (4)). Specific ranges are prescribed for certain properties before and after brazing.