Optimization of pulsed current in resistance spot welding of Zn-coated hot-stamped boron steels

• Published in: Journal of mechanical science and technology Vol. 33; no. 4; pp. 1615 - 1621
• Main Authors: Cheon, Joo Yong, Vijayan, Vijeesh, Murgun, Sivaprasad, Park, Yeong Do, Kim, Jae Hun, Yu, Ji Young, Ji, Changwook
• Format: Journal Article
• Language: English
• Published: Seoul Korean Society of Mechanical Engineers 01-04-2019; Springer Nature B.V; 대한기계학회
• Subjects: Alloying; Boron; Boron steels; Contact resistance; Control; Corrosion resistance; Corrosion resistant steels; Dynamical Systems; Engineering; Expulsion; Industrial and Production Engineering; Low currents; Mechanical Engineering; Mechanical properties; Optimization; Protective coatings; Pulsed current; Resistance spot welding; Spot welds; Stiffness; Vaporization; Vibration; Zinc; Zinc coatings; 기계공학; Pulsed current; Hot-stamped boron steel; Weldability; Metallic coatings; Resistance spot welding
• ISSN: 1738-494X; 1976-3824
• DOI: 10.1007/s12206-019-0313-2

Metallic coatings have been widely used for hot-stamped boron steel in automotive applications. Surface coating in hot-stamped boron steels has improved corrosion resistance. However, a thick coating layer degrades resistance spot weldability. In the case of a Zn-coated hot-stamped boron steel, the high contact resistance and material stiffness with low vaporization temperature of the alloyed layers result in a narrow current passage at the faying surface. Expulsion occurs at low current due to rapid heat development, resulting in a narrow weld current range. The pulsed current can control the heat input by applying a fast cool time during welding to improve the mechanical properties of the joint and acceptable current range. In this study, Zn-coated hot-stamped steels were resistance spot welded using various pulse current procedures, and welding condition was optimized via three pulsed current steps. Step 1: Contact area was controlled without nugget formation. Step 2: Nugget growth was minimized and contact area was maximized. Step 3: The maximum acceptable current range and nugget diameter were achieved. These welding conditions improved the acceptable current range and mechanical properties of spot welds due to increased spot weld size.