Galvanized Welded Joint Plating for Toe Corrosion Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The corrosion resistance of welded joints made from galvanized steel sheets is compromised due to Zn evaporation during welding, leading to blowhole formation and a lack of metal Zn phases in the plating, which reduces corrosion resistance at the toe of the weld.
Innovation Solution
The development of a welded joint with a specific plating layer composition and structure that includes a phase functioning as metal Zn, such as the η-Zn, MgZn2, Mg2Zn3, or MgZn phase, which remains intact even after welding, enhancing corrosion resistance through sacrificial corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If arc welding or laser welding is performed on galvanized steel sheets, then the steel sheets are joined together, but Zn evaporation occurs during welding causing blowhole formation and loss of corrosion resistance at the toe
Solution Approach 1:
The invention changes the chemical composition parameters of the plating layer by controlling the Al content (5-30 mass%) and Mg content (2-15 mass%) within specific ranges. This parameter optimization prevents excessive Zn evaporation during welding while maintaining corrosion resistance, resolving the contradiction between joint strength and corrosion resistance
Solution Approach 2:
The invention creates a composite plating layer structure containing multiple phases (Al-rich phase, Mg-rich phase, and Zn-containing phase) with specific area fraction distributions. This composite structure provides both welding performance and corrosion resistance, eliminating the trade-off between joint strength and corrosion resistance
2Reliability
If the plating layer contains high Zn content to maintain corrosion resistance, then sacrificial corrosion protection is improved, but Zn evaporation during welding increases causing blowhole formation
Solution Approach 1:
The invention optimizes the Al content (5-30 mass%) and Mg content (2-15 mass%) parameters while controlling Zn content to 5 mass% or more but not excessively high. This balanced composition reduces Zn evaporation tendency during welding while preserving sacrificial corrosion protection, resolving the contradiction between corrosion resistance and blowhole prevention
Solution Approach 2:
The invention creates local quality differences by forming distinct phases with different compositions and functions: Al-rich phase for oxidation resistance, Mg-rich phase for corrosion protection, and controlled Zn-containing phase for sacrificial protection. This local differentiation allows the plating to resist corrosion without excessive Zn evaporation during welding
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 proposed solution significantly improves the corrosion resistance in the vicinity of the toe of welded joints by maintaining metal Zn phases during welding, thereby enhancing the structural integrity and durability of galvanized steel welds.
Implementation Method 1
the corrosion resistance in the vicinity of the toe could be further improved due to sacrificial corrosion resistance of metal Zn
Implementation Method 2
a decrease in corrosion resistance due to Zn evaporation in the plating during welding
Data Source
AI summary
To further improve corrosion resistance in the vicinity of a toe.A welded joint according to the present invention includes: a first steel sheet and a second steel sheet; and a weld bead zone formed by arc welding or laser welding, wherein at least one of the first steel sheet or the second steel sheet has a plating layer formed by a predetermined component and an oxide layer located on the plating layer in a non-heat-affected zone, and in a region from a position orthogonal to an extension direction of the weld bead zone from the toe and 1 mm in a direction separating from the toe to a position orthogonal to the extension direction from the toe and 2 mm in the direction separating from the toe, the plating layer has at least one of a η-Zn phase, MgZn2 phase, Mg2Zn3 phase, or MgZn phase as a metal Zn-containing phase having a circle-equivalent diameter of 0.5 μm or more, and when each of the metal Zn-containing phases is projected onto an interface between a base iron and the plating layer, a total sum of lengths of the metal Zn-containing phases in the direction orthogonal to the extension direction, Lt, is 10% or more of a length of the interface, Le.