Weld Flange Pretreatment to Mitigate Zinc-Induced LME Cracking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Liquid metal embrittlement cracking occurs during resistance welding of galvanized high strength steels due to the interaction between molten zinc coatings and the steel, leading to ductility losses and cracking, which is not effectively mitigated by current methods.
Innovation Solution
Applying a zinc-based material in combination with a metallic alloying material having a higher melting point, such as aluminum or nickel, on the steel surfaces before welding, allowing them to alloy and prevent zinc penetration into grain boundaries, thereby reducing the risk of liquid metal embrittlement cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If zinc coating is applied to high strength steel for galvanic protection, then corrosion resistance is improved, but liquid metal embrittlement cracking occurs during resistance welding
Solution Approach 1:
An aluminum-based or nickel-based intermediate layer is introduced between the zinc coating and the steel base metal. This intermediate layer acts as a barrier that prevents molten zinc from penetrating into the grain boundaries of the steel during welding, thereby eliminating the harmful LME effect while preserving the zinc layer's corrosion protection function.
Solution Approach 2:
The coating structure is transformed from a single-layer zinc coating to a multi-layer composite structure consisting of zinc layer plus aluminum-based or nickel-based intermediate layer. This composite coating system combines the corrosion resistance of zinc with the protective barrier properties of aluminum or nickel, solving the LME cracking problem during welding.
2Productivity
If rapid resistance welding is used to join high strength steel components, then productivity is improved, but liquid metal embrittlement cracking occurs due to molten zinc interaction with steel
Solution Approach 1:
The aluminum-based or nickel-based intermediate layer serves as a protective mediator that allows rapid resistance welding to proceed without causing LME cracking. It blocks the interaction between molten zinc and the steel grain boundaries, enabling high-speed welding while preventing the harmful effect.
3Reliability
If zinc coating thickness is increased to improve corrosion protection, then reliability is improved, but the risk of liquid metal embrittlement cracking during welding increases
Solution Approach 1:
The aluminum-based or nickel-based intermediate layer acts as a permanent barrier that prevents zinc penetration regardless of zinc layer thickness. This allows the use of thicker zinc coatings for enhanced corrosion protection without increasing the risk of LME cracking, as the intermediate layer blocks zinc from reaching the grain boundaries.
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 alloying process effectively raises the melting point and prevents zinc from causing cracks in the steel, significantly reducing or eliminating liquid metal embrittlement cracking during resistance welding of galvanized steels, ensuring stronger welds and improved structural integrity.
Implementation Method 1
the zinc and the other metallic material alloy together to substantially prevent the zinc from penetrating into the grain boundaries of the workpieces
Implementation Method 2
locally elevates temperatures at the weld sites to approximately 1500 degrees Celsius or higher. When zinc coated HSS components are welded, liquid zinc, which melts at approximately 400 degrees Celsius
Data Source
AI summary
A method of forming an assembly includes providing a metallic first workpiece having base and a first layer disposed on the base and adhering a second layer onto the first layer. One of the first and second layers is formed of a zinc-based material formed of at least a majority of zinc, and the other of the first and second layers is formed of a metallic alloying material having a melting point higher than the melting point of the zinc-based material. Preferably, the first layer is formed of the zinc-based material, and the second layer is formed of the metallic alloying material with the higher melting point. A metallic second workpiece is disposed in contact with the second layer. A welding operation is performed to join the first workpiece to the second workpiece. A welded assembly is also provided.