Brazed Heat Exchanger Baseplate Alloy for LFM-Resistant Joints
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Solution Overview
Problem
Aluminium alloys commonly used in brazed heat exchanger assemblies, such as 5XXX, 6XXX, and 7XXX-series, are prone to metallographic braze-related defects like excessive Si diffusion and Liquid Film Migration (LFM), which compromise joint quality and structural integrity.
Innovation Solution
An age-hardenable 3XXX-series aluminium alloy with a specific composition (Mn 0.8% - 1.8%, Cu 0.45% - 1.20%, Si 0.25% - 1.30%, Mg 0.10% - 0.60%, Fe up to 0.8%, Zn up to 0.3%, Ti up to 0.20%, Cr up to 0.25%, and balance aluminium) is used for the baseplate, offering increased post-braze strength and improved brazability, reducing Si diffusion and LFM issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If 5XXX, 6XXX, or 7XXX-series aluminium alloys are used for the baseplate, then the baseplate can be manufactured with common aluminium alloy processes, but the alloy is prone to excessive Si diffusion and Liquid Film Migration during brazing, compromising joint quality
Solution Approach 1:
The patent changes the chemical composition parameters of the aluminium alloy baseplate by specifying precise ranges for Si (0.25-1.30%), Mn (0.80-1.80%), Cu (0.45-1.20%), and other elements. This parameter optimization prevents excessive Si diffusion and Liquid Film Migration during brazing while maintaining manufacturability through conventional aluminium alloy processes
Solution Approach 2:
The patent creates a composite aluminium alloy system combining multiple elements (Al-Si-Mn-Cu-Mg-Fe-Zn-Ti-Cr-Zr) in specific proportions. This composite alloy structure achieves both good brazability and resistance to Si diffusion/LFM, resolving the contradiction between ease of manufacture and joint quality reliability
2Strength
If the baseplate is made thicker to ensure structural integrity, then the strength and stiffness are improved, but the weight of the heat exchanger assembly increases
Solution Approach 1:
The patent optimizes the alloy composition parameters to achieve superior strength-to-weight ratio. The specific composition ranges (particularly Cu+Mg>1.0%, Mn 0.80-1.80%) enable the baseplate to attain high strength properties, allowing thinner gauge materials that reduce weight while maintaining structural integrity
3Reliability
If protective cladding materials are applied to the baseplate to prevent Si diffusion and LFM, then the joint quality is improved, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent changes the baseplate material parameters by optimizing the aluminium alloy composition to inherently resist Si diffusion and Liquid Film Migration. This eliminates the need for protective cladding materials, reducing manufacturing complexity while maintaining joint quality through conventional aluminium alloy processing
Solution Approach 2:
The patent extracts and removes the protective cladding layer from the baseplate structure by developing an alloy composition that provides inherent protection against brazing defects. This simplifies the overall structure and manufacturing process while maintaining reliability
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 solution provides enhanced post-braze strength, joint strength, and resistance to LFM, enabling the use of thinner gauge baseplates and improving the overall structural integrity of brazed heat exchanger assemblies, while avoiding the need for protective cladding materials.
Implementation Method 1
The baseplate is made of an age-hardenable 3XXX-series aluminium alloy
Implementation Method 2
The various components are commonly joined to each other by brazing. In a brazing process, a brazing filler metal or brazing alloy is applied to at least one portion of the substrate to be brazed
Implementation Method 3
the heat exchanger subjected to a brazing cycle to interconnect the various components together into a unitary brazed assembly
Data Source
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AI summary
The invention relates to a brazed heat exchanger incorporating an aluminium alloy baseplate and wherein the baseplate is made from an aluminium alloy having a composition, in wt.%, of:Mn 0.8-1.8, Cu 0.15-1.20, Si 0.25–1.30, Mg 0.10-0.60, Fe ≤0.8, Zn ≤0.3, Ti ≤0.20, Cr ≤ 0.25, Zr ≤0.25,balance aluminium and impurities.