1. Introduction
- Automobile undercarriage components are exposed to extremely severe corrosive environments in which mud, water or even the salt used as a snow melting agent in cold regions splashes up from the road and adheres to them.
- As corrosion progresses, steel sheets undergo thinning, resulting in a reduction of their designed strength and rigidity, or, at worst, threatening the vehicle’ s safety if a component were to break.
- In order to increase corrosion resistance of undercarriage components, electrodeposition coating is performed.
- However, coating defects easily occur at the welded zone.
- To enhance the electrodeposition coating properties, MIX-1TR have been developed by focusing on both coating and welding technologies.
2. The mechanism of corrosion on undercarriage components
- A thorough coating film might not necessarily be formed because electrodeposition coating on the surface of actual components may be obstructed by slag or fumes, causing coating defects or reducing the adhesion of coating films.
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If slag, which is an oxide and is low in electric conductivity, remains on the weld, the electrodeposition coating film seldom forms as shown in Figures 1 and 2.
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This is where rust initiates and corrosion begins to make progress.
3. Electrodeposition coating property of MIX-1TR
Slag consists of oxides of Si and Mn (usually contained in welding consumables as well as in steel plates) that are formed by combining with oxygen in the shielding gas during welding.
one way to lessen slag generation to a certain degree is by reducing (but not eliminating) the oxygen source in the shielding gas.
A better solution is MIX-1TR, which works not by restraining slag generation but by producing slag and slag components that do not damage electrodeposition coating properties.
In addition, the slag generated with the conventional solid wire appears fragile and easy to peel off, which could be problematic if slag, together with the coating film, detaches during the running of a vehicle; those small parts without coating film might expand and corrosion would make quick progress.
Slag generated with MIX-1TR is excellent adhesion to weld beads. In fact, adhesion to the weld bead is so strong that the slag will not detach when physically hit - even by a hammer.
4. Features of MIX-1TR
- MIX-1TR is best suited to welding 440-780 Mpa class thin steel sheets for automobile production.
- MIX-1TR was developed to be applied in pulsed welding with Ar+CO2 shielding gas.
- The tensile strength and impact properties of MIX-1TR are better than those of conventional solid wire.
5. Tolerance for root gap & Wire Position are superior to Conventional wire.
- Penetration and bead configuration are important for welding undercarriage components, which are required to carry loads continuously.
- In actual welding of undercarriage components, weld gaps frequently occur because of the unevenness of component-shapes as a result of how they were pressed during fabrication.
- It is, therefore, necessary to produce sound bead shapes even though a certain degree of gap may exist. Additionally, preventing undercut during welding is essential because it contributes to a decrease in fatigue strength.
- in the welding of a test specimen with a 1 mm gap, MIX-1TR did not cause undercut, while the conventional solid wire clearly generated undercut at the toe of the lower side steel sheet.
6. Bead Shape in Horizontal Position is superior to Conventional wire. Suitable for high-Speed Welding.
- Automobile components are frequently welded at relatively fast speeds, which can cause beads to become more convex in shape as a result of the lower heat input. However, because a convex bead shape leads directly to reducing fatigue strength, producing such shapes must be avoided.
- When the conventional solid wire was used, the bead shapes gradually became convex as the welding speed increased; however, beads produced by MIX-1TR varied little and remained stable despite increasing welding speed.
6. Conclusion
MIX-1TR, is a solid wire for MAG welding that is superior to conventional wires in producing auto components with excellent corrosion resistance. It offers the following advantages:
- Welds are provided with substantially improved electrodeposition coating properties.
- Undercut is not likely to occur at the toe of the welded bead even in the welding of steel sheets with gaps.
- Bead configuration is not likely to become convex even in high-speed welding.
- Stable welding with little spatter is possible by selecting optimum welding parameters.
