Multiply-Clad Brazing Sheet for Corrosion-Resistant Heat Exchangers
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Solution Overview
Problem
Heat exchanger tubes and plates made of aluminum alloys face challenges in severe corrosive environments, such as those created by recirculated exhaust gases, due to silicon diffusion from brazing alloys degrading corrosion resistance, and existing solutions like multi-clad sheets or surface treatments are either insufficient or too costly.
Innovation Solution
A brazing sheet with a recrystallized structure and controlled anti-recrystallizing elements, featuring an intermediate layer with specific composition and a core alloy from the AA3xxx series, optimized for improved corrosion resistance and manufacturability, including a homogenization process and specific element content to enhance hot flow stress and corrosion behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If AA4xxx series brazing alloy plating is applied to aluminum alloy heat exchanger tubes, then brazing capability is improved, but silicon diffusion degrades corrosion resistance
Solution Approach 1:
An intermediate plating layer composed of Al-Si-Mg alloy is introduced between the AA3xxx series core alloy and the AA4xxx series brazing alloy plating. This intermediate layer acts as a diffusion barrier that prevents silicon from the brazing alloy from diffusing into the core alloy during the brazing process, thereby maintaining the corrosion resistance of the core while enabling effective brazing through the outer AA4xxx plating layer.
2Reliability
If multi-clad sheets with intermediate plating are used to improve corrosion resistance, then corrosion behavior is enhanced, but manufacturing complexity increases
Solution Approach 1:
The intermediate plating layer is designed with specific compositional parameters (Al-Si-Mg alloy with controlled silicon and magnesium content) and thickness parameters (5-20 micrometers) that optimize both corrosion resistance and manufacturability. By carefully controlling these parameters, the intermediate layer provides sufficient protection against silicon diffusion while remaining thin enough to be applied efficiently during the brazing process, thus balancing performance enhancement with manufacturing simplicity.
3Reliability
If sacrificial protective plating of AA1xxx or AA7xxx series is used, then corrosion resistance is improved, but brazing capability on both sides is lost
Solution Approach 1:
The plating structure is designed with different functional qualities at different locations: the intermediate layer (Al-Si-Mg alloy) provides corrosion protection and diffusion barrier properties, while the outer AA4xxx series plating layer provides brazing capability. This spatial differentiation of functions allows the heat exchanger tube to achieve both corrosion resistance and brazing capability on both sides, overcoming the limitation of using sacrificial protective plating alone.
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 corrosion resistance and manufacturability, with brazing sheets exhibiting a lifespan of over 8 weeks in SWAAT tests and improved performance in acidic environments, balancing rolling ability and corrosion resistance.
Implementation Method 1
the plate intended for the manufacture of the core sheet undergoes, after casting and peeling, and before rolling, homogenization at a temperature of 550 to 630°C for at least one hour
Implementation Method 2
a significant diffusion of silicon, contained in the plating alloy of the AA4xxx series, towards the core alloy constituting the core of the tube occurs during the brazing operation
Implementation Method 3
generally from the AA4xxx series. This has the advantage of melting at a temperature lower than the melting temperature of the core and, by applying a thermal brazing cycle, of being able to create a bond between two materials to be assembled
Data Source
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AI summary
The invention relates to a brazing metal sheet consisting of a series AA3xxx aluminum alloy core sheet, coated, on at least one surface, with a cladding layer made of a first so-called "intermediate aluminum alloy" containing 0.35 to 1.8 wt% manganese, less than 0.3 wt% of each of other elements, and a total of 1 wt% aluminum residue. Said series AA3xxx cladding layer is itself coated with a second series AA4xxx alloy cladding layer in which the alloy of the core metal sheet is selected, and the core metal sheet developed, such as to have an essentially recrystallized structure after brazing. The invention also relates to the use of such a metal sheet for manufacturing a "supercharge air cooler" heat exchanger or passenger compartment air conditioner "evaporator" heat exchanger, and to said exchangers themselves, manufactured from said metal sheets.