Cu-Al Welded Joint Microstructure for Higher Joining Strength
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Solution Overview
Problem
The existing metal member-welded structures formed by connecting copper (Cu) and aluminum (Al) members lack sufficient joining strength, which is a critical issue in applications requiring high bonding integrity.
Innovation Solution
A metal member-welded structure is developed with a sea-island structure at the interface, where the Cu member has a Cu-based material and an Al member with a plating layer, welded using a laser with specific conditions (output of 550 W or more and scanning rate of 10 mm/sec or more) to form a eutectic structure with intermetallic compounds and pure Al phases, enhancing ductility and stress distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional welding methods are used to join Cu and Al members, then the manufacturing process is simple, but the joining strength is insufficient
Solution Approach 1:
The invention changes the welding parameters by applying laser with specific output (550W or more) and scanning rate (10mm/sec or more) to achieve a sea-island structure in the welded portion, thereby improving joining strength without requiring complex additional process steps
Solution Approach 2:
The invention creates a composite microstructure in the welded portion consisting of pure Al island portions dispersed in a eutectic sea portion containing intermetallic compounds and pure Al, which enhances the joining strength through the combined properties of different phases
2Strength
If high joining strength is achieved through conventional methods, then the bonding integrity is improved, but the ductility and stress distribution are compromised
Solution Approach 1:
The invention creates local quality variations within the welded portion by forming discrete pure Al island portions with high ductility dispersed in the eutectic sea portion, allowing different regions to fulfill different functional requirements for strength and ductility
Solution Approach 2:
The sea-island structure forms a composite material system where the pure Al island portions provide ductility and the eutectic sea portion provides strength, achieving a balance between bonding integrity and mechanical flexibility
3Strength
If the Cu member is partially melted to improve bonding, then the joining strength is enhanced, but the formation of fragile intermetallic compounds increases
Solution Approach 1:
The invention precisely controls the laser welding parameters (output of 550W or more, scanning rate of 10mm/sec or more) to achieve partial melting of Cu while controlling the cooling rate to form a eutectic structure that reduces the amount of fragile intermetallic compounds compared to conventional methods
Solution Approach 2:
The invention utilizes phase transition during rapid cooling after laser welding to form a eutectic structure in the sea portion, where the phase transformation from liquid to solid creates a fine microstructure with reduced intermetallic compound formation
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 method significantly improves the joining strength between Cu and Al members by creating a sea-island structure that distributes stress effectively and suppresses the formation of fragile intermetallic compounds, resulting in a structure with enhanced mechanical properties comparable to partial melting of the Cu member.
Implementation Method 1
laser is applied from an Al member side to the Cu member
Implementation Method 2
a welded portion formed by melting and solidifying each of materials of the Cu member and the Al member
Implementation Method 3
the sea portion has a eutectic structure having a phase of an intermetallic compound of Cu and Al, and a phase of pure Al
Data Source
AI summary
A metal member-welded structure includes: a Cu member; an Al member; and a welded portion formed by melting and solidifying each of materials of the Cu member and the Al member. The Cu member includes a Cu-based material containing Cu as a main component. The Al member includes an Al-based material containing Al as a main component and a plating layer that covers a side of the Al-based material, the side being close to a surface of the Cu member. The welded portion includes a sea-island structure in a vicinity of the surface of the Cu member. The sea-island structure includes: a plurality of island portions containing pure Al, and a sea portion interposed among the island portions. The sea portion has a eutectic structure having: a phase of an intermetallic compound of Cu and Al; and a phase of pure Al.