Effect of Al-Si Coating on Weldability of Press-Hardened Steels
- 43 Downloads
Resistance spot welding (RSW) of Al-Si-coated PHS was undertaken, and the effect of Al-Si coating on nugget formation and mechanical properties was investigated. Press-hardened steel (PHS) has long been applied to automotive body structure construction to support mass and corresponding greenhouse gas emission reductions. PHS materials are often combined with an Al-Si coating applied as an oxidation barrier though unfortunately, the Al-Si coating poses a challenge to the resistance spot welding (RSW) of PHS containing stack-ups. As a newly developed coating for the hot stamping process, the property of Al-Si coating is different from base metal and traditional coatings, and the influence mechanism of Al-Si coating on the welding process is not clear. It would remain at nugget edge and might cause severe stress concentration. To investigate this problem, RSW of 1.5-mm Al-Si-coated PHS was undertaken, and the results indicate that a large portion of the Al-Si coating is extruded and forms a sharp notch close to the nugget edge during the welding process. During the post-weld cooling stage, a thin layer of residual coating is formed between the nugget and notch root. The mechanical performance of the welded joints is limited by the thin residual Al-Si layer which acts as a preexisting crack and supports the interfacial fracture. The presence of the Al-Si coating at the faying interface also significantly delays nugget formation, though it contributes to a larger nugget size by inhibiting expulsion events at the faying interface.
KeywordsAl-Si coating press-hardened steel resistance spot welding ultrahigh-strength steel
The authors would like to acknowledge the supports of GM Research and Development Center. The authors gratefully acknowledge the supports of National Natural Science Foundation of China (Grant Nos. U1564204, U1764251, and 51805323).
- 4.Y. Li, H.W. Liu, Y.H. Du, and P. Zhang, Applications and Developments of AHSS in Automobile Industry, Mater. Rev. A, 2011, 25(7), p 101–104 (in Chinese)Google Scholar
- 5.J. Lechler and M. Merklein, Hot Stamping of Ultra High Strength Steels as a Key Technology for Lightweight Construction, Mater. Sci. Technol., 2008, 9, p 1698–1709Google Scholar
- 7.M. Merklein, J. Lechler, and T. Stoehr, Characterization of Tribological and Thermal Properties of Metallic Coatings for hot Stamping Boron Manganese Steels. Proceedings of the Seventh International Conference on Coatings in Manufacturing Engineering, (2008), pp. 1–3Google Scholar
- 8.N.N., Stahl-Informations-Zentrum. Stahl im Automobil, Leicht und sicher, 2009. www.stahl-info.de.
- 10.P. Drillet, R. Grigorieva, G. Leuillier, et al., Study of Cracks Propagation Inside the Steel on Press Hardened Steel Zinc Based Coatings. La Metallurgia Italiana 1 (2013)Google Scholar
- 13.S.J. Chen, Y. Yu, C. Wang et al., Study on Spot Welding of UHSS Using IF Inverter and Servo Welding Gun System, Dianhanji Electr. Weld. Mach., 2010, 40(5), p 70–73Google Scholar
- 21.T. Heumann and S. Dittrich, Effect of Bevel Angle on Microstructure and Mechanical Property of Al/Steel Butt Joint Using Laser Welding-Brazing Method, Z. Met., 1959, 50, p 617–625Google Scholar