Dissimilar Metal Joint Welding by Expelling Low-Melting Interlayers
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Solution Overview
Problem
The existing electric resistance welding methods for dissimilar metals, such as steel and aluminum or magnesium alloys, often result in low welding strength due to the formation of brittle intermetallic compounds and a tendency for cracks, especially when welding high-strength steel with aluminum or magnesium alloys, which affects the mechanical strength of the joints.
Innovation Solution
An electric resistance welding method that involves a laminated structure with first-class metal plates made of pure iron or iron-based alloys and a second-class metal plate with a density less than 5 g/cm3 or a melting point below 800°C, where an expulsion current and electrode pressure are applied to heat and separate the second-class metal from the welding region in a splashing mode, allowing only first-class metal plates to form a metallurgical connection, thereby avoiding brittle intermetallic compounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional electric resistance welding is used to weld steel and aluminum/magnesium alloys, then welding connection is achieved, but brittle intermetallic compounds form and welding strength decreases
Solution Approach 1:
The patent extracts and removes the harmful second-class metal (aluminum or magnesium alloy) from the welding region through controlled melting and ejection. The expulsion current melts the second-class metal plate, and the pressure difference ejects the molten metal out of the welding region, preventing intermetallic compound formation while maintaining the connection between first-class metal plates
Solution Approach 2:
The patent changes the physical state of the second-class metal from solid to liquid through controlled heating with expulsion current. By precisely controlling the temperature parameter to melt only the second-class metal (melting point <800°C) while keeping the first-class metal plates solid, the process enables selective removal of harmful material without affecting the structural metals
2Strength
If high temperature heating is applied to weld dissimilar metals, then metallurgical connection is achieved, but crack formation increases due to prolonged exposure
Solution Approach 1:
The patent rushes through the high-temperature exposure phase by quickly melting and ejecting the second-class metal before it can form extensive intermetallic compounds or cause thermal damage. The expulsion current applies intense heating for a brief period, rapidly transitioning the second-class metal to liquid state and ejecting it, thereby minimizing the duration of harmful thermal exposure
Solution Approach 2:
The patent performs preliminary melting of the second-class metal plate before the main welding connection is established. By pre-melting and ejecting the harmful material, the subsequent welding process operates on a cleaner interface between first-class metal plates, preventing crack formation from the start
3Stability of the object's composition
If aluminum/magnesium alloy is kept in welding region during welding, then joint structure is maintained, but welding quality deteriorates due to intermetallic compound formation
Solution Approach 1:
The patent converts the harmful presence of aluminum/magnesium alloy into a beneficial process feature. The low melting point of the second-class metal, which normally causes intermetallic compound formation, is exploited to enable selective melting and ejection. The harmful material becomes the vehicle for its own removal, transforming a welding defect into the mechanism for achieving high-quality joints
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 effectively prevents the formation of brittle intermetallic compounds, enhances welding quality, and achieves a strong, reliable connection between dissimilar metals by ensuring only a trace amount of second-class metal remains in the welding interface, improving the mechanical properties and service life of the joint.
Implementation Method 1
an expulsion current and an electrode pressure are applied to a laminated structure, so that a laminated structure in a welding region is heated
Implementation Method 2
the second-class metal plate is made of an elementary substance or an alloy with a density of less than 5 g/cm3 or a melting point of lower than 800° C.
Implementation Method 3
an expulsion current and an electrode pressure are applied to a laminated structure, so that the laminated structure in the welding region is heated
Data Source
AI summary
An electric resistance welding method for a dissimilar metal joint used for welding a laminated structure, with an outer layer being composed of iron or iron-based alloy, and an inner layer being composed of a metal with a density of less than 5 g/cm3 or a melting point of lower than 800° C. The electric resistance welding method comprises an expulsion stage in which a light metal or low-melting-point metal in the middle of the laminated structure is separated in a splashing mode, so that a connecting structure is directly formed between iron or iron-based alloy layers in a welding interface to complete welding. According to the invention, the formation of brittle intermetallic compounds on the welding interface of the dissimilar joint can be avoided, thereby improving the mechanical properties of the joint and achieving reliable connection between dissimilar metals. The invention further provides a dissimilar metal joint.