Welding Galvanized Steel -- Safely

JFE TECHNICAL REPORT No. 4 (Nov. 2004)

Hot-Dip Galvanized Steel Sheet with Excellent Surface Quality for Automotive Outer Panels†

TOBIYAMA Yoichi*1 ABOTANI Kazuhiro*2

Abstract: A new type, hot-dip galvanized steel sheet (GI) with excellent press formability, weldability, and surface appearance was developed for automotive outer panels. The sliding characteristics of GI in press forming were improved by optimizing surface roughness by texture control in skinpass rolling and use of a high-lubricity anti-rust oil, while spot welding electrode life was extended by selecting a suitable substrate chemistry. Many process improvements were also adopted to improve the surface quality of GI for use of automotive outer panels. They included adjustment of wiping conditions to prevent bath wrinkle pattern, adoption of an exclusive bath for GI with an appropriate Al content to prevent dross adherence, and control of the cooling rate after galvanizing to produce a stable minimum spangle coating. The developed GI is now in commercial production.

selectively to take advantage of their respective features. Although European automakers use electrogalvanized (EG) and galvannealed (GA) steel sheets, non-alloy hotdip galvanized sheets (GI) continue to represent the mainstream. Moreover, in recent years, the number of makers who apply GI not only to inner panels, but also to outer panels, has continued to increase, supporting growing demand.1) Hot-dip galvanized sheets have long enjoyed advantages over EG, in which GI with heavy coating weights can be produced more easily and production costs are lower. On the other hand, improvement of various properties of GI, including surface quality and press formability, has been required for application to outer panels. This paper describes the quality features and production technology of a newly developed GI which solves these problems and has been successfully applied to automotive outer panels.

1. Introduction

As a measure to...