Butt Welding Zinc-Coated Steel Sheets Without LME Cracking

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Solution Overview

Problem

The manufacturing of laser welded blanks using zinc coated steels with high strength and formability poses challenges due to liquid metal embrittlement (LME) risks in the weld seam, which can lead to structural weaknesses and cracks.

Innovation Solution

A method involving the removal of at least part of the zinc-based metallic coating from steel sheets with a thickness above 3.5 microns, particularly in areas with high Carbon or Silicon content, to create an ablation area before welding, ensuring the zinc coating thickness after ablation is equal to or lower than 3.5 microns, and the ablation area width after welding is equal to or greater than 0.5 mm.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If zinc coating is applied for corrosion protection, then corrosion resistance is improved, but liquid metal embrittlement occurs during welding

Engineering Contradiction:

Improvecorrosion resistanceVSAvoidliquid metal embrittlement

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The zinc coating is removed from the welding area before the welding process takes place. This preliminary action prevents the zinc from causing liquid metal embrittlement during welding, while the rest of the coating remains intact to provide corrosion protection throughout the component's service life.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The zinc coating is selectively removed only from the specific welding area where it would cause harm, while maintaining the coating in other areas where it provides beneficial corrosion protection. This creates different surface conditions in different locations of the same component.

Inventive Principle:

Principle #3Local quality

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 effectively prevents liquid metal embrittlement (LME) in the weld seam, ensuring reliable resistance and formability of the laser welded blanks without structural weaknesses, thereby enhancing the safety and durability of the final parts.

Implementation Method 1

butt welding said steel sheets (1, 2) using at least a laser source

Methodology Applied

Scientific EffectLaser welding: Laser Beam Welding

Implementation Method 2

removing at least part of said metallic coating to form an ablation area before welding (6)

Methodology Applied

Scientific EffectAblation: Laser Ablation

Data Source

PatentUS20250033147A1Method for butt-welding a steel part and associated steel part

Publication Date: 2025.01.30 ARCELORMITTAL SA

AI summary

Method for butt-welding two steel sheets including the steps of providing two steel sheets (1, 2), on all the faces having a zinc based metallic coating thickness Znth above 3.5 microns and a steel sheet substrate (12) with a Carbon content above 0.15% or a Silicon content above 0.5% or both: removing at least part of-the metallic coating to form an ablation area before welding (6) having a Zinc-based metallic coating thickness after ablation Znab which is equal to or lower than 3.5 microns and in such a way that the width of the ablation area after welding (8) is equal to or greater than 0.5 mm, butt welding the steel sheets (1, 2) using at least a laser source.