Cu-Zn Brazed Junction Structure for Void-Suppressed Motor Bonding
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Solution Overview
Problem
The bonded structure using a Cu-based bonding object and a Zn-based brazing filler metal experiences increased contact resistance at high temperatures, leading to conduction failures, with existing technologies lacking a clear mechanism and countermeasure for this issue.
Innovation Solution
Controlling the maximum achieving temperature during brazing to less than 560 °C to suppress the formation of the CuZn3 alloy phase at the bonded interface, thereby reducing void formation and enhancing bonding reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a Zn-based brazing filler metal is used to bond a Cu-based bonding object, then the melting point is reduced and operation property is improved, but contact resistance increases at high temperatures due to formation of CuZn3 alloy phase and voids
Solution Approach 1:
The invention changes the chemical composition parameters of the Zn-based brazing filler metal by adding specific amounts of Al (3-15 wt%) and Si (0.1-5 wt%). This compositional modification alters the phase formation behavior during brazing, suppressing the formation of the harmful CuZn3 alloy phase while maintaining low melting point and good fluidity for reliable bonding.
2Ease of manufacture
If a Zn-based brazing filler metal is used to bond a Cu-based bonding object, then the bonding process is simplified, but void formation occurs at the bonded interface leading to conduction failures
Solution Approach 1:
The invention introduces Al and Si as intermediary elements that modify the brazing filler metal's interaction with Cu. Al promotes wetting and forms a transition layer, while Si suppresses excessive intermetallic growth. These intermediaries prevent direct formation of large voids at the Cu-Zn interface, reducing conduction failures while keeping the bonding process simple.
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 approach results in a bonded structure with high bonding reliability and minimal change in contact resistance during high-temperature energization operations, effectively preventing conduction failures.
Implementation Method 1
Zn itself has a melting point of 420 °C, but forms a eutectic alloy when about 5 wt% of Al is added thereto, and its melting point is reduced to about 380 °C
Implementation Method 2
diffusion bonding is performed at 420 °C by using a Zn-Al alloy as a material alloy of an insert material
Implementation Method 3
the Zn layer and the Cu layer react with each other to form a CuZn5 layer and a Cu5Zn8 layer at an interface between the Zn layer and the Cu layer
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
Provided is a bonded structure, including a Cu-based bonding object (1) bonded with a Zn-based brazing filler metal (2), wherein the bonded structure includes a joint including a first alloy phase (3), a second alloy phase (4), and a third alloy phase (5) between the Zn-based brazing filler metal (2) and the Cu-based bonding object (1), wherein the first alloy phase (3) is an alloy phase having a basic composition of Cu5Zn8, wherein the third alloy phase (5) is an alloy phase having a basic composition of CuZn4 or CuZn5 in which part thereof is in contact with the first alloy phase (3), wherein the second alloy phase (4) is an alloy phase having a basic composition of CuZn3 and being formed at an interface between the first alloy phase and the third alloy phase (5), and wherein, in a cross section parallel to a bonding direction, a ratio of the second alloy phase (4) at the interface between the first alloy phase (3) and the third alloy phase (5) is less than 80 %. With this, a bonded structure in which formation of voids is suppressed in the joint between the Zn-based brazing filler metal (2) and the Cu-based bonding object (1), and which has high bonding reliability can be obtained.