Brazing Metallic Substrates by Activating Oxide Layer Removal
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The formation of a passive metal oxide layer on metallic substrates, such as aluminum or titanium, hinders proper wetting and flow of filler materials during brazing, resulting in uneven and weak brazing joints, as existing methods like machining or using reactive elements in filler materials have limitations.
Innovation Solution
Grit blasting powdered activating materials, such as silicon carbide, onto the substrate surface at elevated pressure to break down the oxide layer, combined with machining to remove excess oxide and using filler materials with boron, silicon, or phosphorus to enhance wetting, while maintaining a brazing temperature between 900°C to 1260°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the surface of the metallic substrate is machined to remove the passive oxide layer, then the surface becomes active to wet properly with the filler material, but the oxide layer reforms quickly when the machined surface is exposed to the atmosphere
Solution Approach 1:
The surface is machined in advance to remove the oxide layer before brazing, creating a fresh active surface. This preliminary action ensures the surface is ready for immediate brazing operation, maximizing wetting quality while minimizing re-oxidation time by performing the activation step before exposure to atmosphere during handling
Solution Approach 2:
The process moves quickly from machining to brazing without prolonged exposure of the activated surface to atmosphere. The rapid transition minimizes the window for re-oxidation, effectively skipping the problematic intermediate state where the surface is active but exposed to air
2Reliability
If reactive elements like phosphorus, boron and silicon are used in the filler material to dissolve the oxide layer, then the surface becomes active for wetting, but detrimental brittle phases form within the braze joints
Solution Approach 1:
The harmful oxide layer is mechanically removed from the surface through machining before brazing, extracting the barrier to wetting. This eliminates the need to use reactive elements in the filler material that would otherwise be required to chemically dissolve the oxide, thereby avoiding the formation of brittle phases while still achieving good wetting
Solution Approach 2:
The machining process acts as an intermediary step between the substrate and brazing, preparing the surface by removing the oxide layer. This intermediate mechanical preparation replaces the need for chemical action by reactive filler elements, achieving the same wetting improvement without the harmful side effects
3Ease of operation
If the filler material is brought slightly above its melting temperature for proper distribution, then the filler material flows and wets the surface, but the passive oxide layer prevents proper wetting resulting in uneven and weak brazing
Solution Approach 1:
The oxide layer is removed in advance through machining before the brazing process begins. This preliminary surface preparation ensures that when the filler material is applied at elevated temperature, the active metal surface is already exposed and ready to accept the filler, guaranteeing proper wetting and flow without the interference of the passive oxide barrier
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 method significantly improves the wetting and flow of filler materials, resulting in stronger and more reliable brazed surfaces with reduced porosity and maintaining electrical properties by effectively dissolving the passive oxide layer at brazing temperatures.
Implementation Method 1
The activating material acts as a catalyst that splits into its constituents at brazing temperature to break up or dissolve the metal oxide layer
Implementation Method 2
a filler material is heated to its melting temperature and distributed over a surface of a metallic substrate by capillary action
Implementation Method 3
the grit blasting of said powdered particles of the activating material on said surface is done at a pressure between 3 bar - 6 bar
Implementation Method 4
the brazing temperature is kept in the range of 900° C to 1260° C. This helps to provide sufficient heat to the filler material to melt for wetting and providing heat to dissociate the activating material
Data Source
Figure 1~2
Figure 3A~3B
AI summary
A method (8) for brazing a surface (10) of a metallic substrate (12) having a generally passive metal oxide layer (18) including steps for activating said surface (10) of said metallic substrate (12) by machining said metallic substrate (12) with a hard metal tool, grit blasting powdered particles (14) of an activating material on said surface (10), and wetting the grit blasted surface (10) of the metallic substrate (12) with a filler material (16) at a brazing temperature, wherein said activating material is reactive with said metal oxide layer (18) at said brazing temperature.