Spot Welding Zinc-Plated Steel to Suppress LME Cracks
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Solution Overview
Problem
Zinc plated steel sheets with ultra-high strength are prone to welding liquid metal embrittlement (LME) cracks during spot welding due to molten zinc penetrating into the grain boundary, which existing methods struggle to effectively suppress.
Innovation Solution
Interposing a filler metal between the zinc plated steel sheet and the welding rod electrode during spot welding, allowing alloying to form an Al—Fe—Zn—Mn intermetallic compound alloy phase at the interface, increasing the melting point and enhancing cracking resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If spot welding is performed on zinc plated steel sheets with ultra-high strength, then welding strength is improved, but welding liquid metal embrittlement cracks occur due to molten zinc penetrating into grain boundaries
Solution Approach 1:
A filler metal (aluminum foil) is introduced as an intermediary material between the zinc plating layer and the welding electrode. This filler metal forms an Al-Fe-Zn-Mn intermetallic compound alloy phase that acts as a barrier, preventing molten zinc from penetrating into the grain boundaries of the base steel sheet during spot welding, thereby eliminating LME cracks while maintaining welding strength
Solution Approach 2:
The chemical composition of the plating layer interface is changed by forming an Al-Fe-Zn-Mn intermetallic compound alloy phase with specific composition (40-60 wt% Fe and Mn). This parameter change in the plating layer composition creates a high-melting-point alloy phase that prevents zinc penetration and suppresses LME cracking
2Reliability
If grain size refinement is used to disperse stress and prevent LME cracks, then some cracking resistance is improved, but the suppression of LME cracks remains insufficient
Solution Approach 1:
The plating layer is transformed into a composite structure containing Al-Fe-Zn-Mn intermetallic compound alloy phases distributed within the zinc matrix. This composite plating layer provides superior LME crack suppression compared to simple grain size refinement, as the intermetallic compounds create a robust barrier against zinc penetration while maintaining structural integrity
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 effectively suppresses welding LME cracks by forming a high-melting-point Al—Fe—Zn—Mn intermetallic compound alloy phase, ensuring excellent cracking resistance in the welded structure.
Implementation Method 1
alloying between the zinc plating layer and the filler metal proceeds during the spot welding to form an Al—Fe—Zn—Mn intermetallic compound alloy phase
Implementation Method 2
form an Al—Fe—Zn—Mn intermetallic compound alloy phase at an interface between the zinc plating layer and the base steel sheet
Implementation Method 3
performing spot welding
Implementation Method 4
interposing a filler metal between the material to be welded and the welding rod electrode and performing spot welding
Data Source
AI summary
An aspect of the present disclosure is to provide a method for manufacturing a welded structure capable of effectively suppressing welding LME cracks generated during spot welding of a zinc plated steel sheet having ultra-high strength, and a welded structure manufactured using the same.