In the automobile industry, significant efforts to reduce the weight of car bodies have been made with fuel economy in mind. Tailored blanks (TBs) are widely used for automobile bodies, which achieve not only weight reduction but also maintain crashworthiness and rigidity for an auto body, hence their application for auto parts will continue increasing in future. Most tailored blanks consist of high strength steel sheets welded in a butt joint. The high strength steel, of which the tensile strength is 590MPa or more, is usually strengthened by transformation hardening. When the high strength steel sheets are welded, the weld metal becomes harder than the base metal, due to the heat input and subsequent rapid cooling during the welding, while the Heat affected zone (HAZ) is possibly caused by temper softening. There is a possibility of formability changing depending on the hardness distribution in the weld zone. The hardness distribution varies according to the welding method used for the tailored blank production. The formability of tailored blanks is known to deteriorate with an increase in the weld metal hardness. However, the influence of the HAZ hardness on formability has not been discussed in as much detail. In the present study, the relationship between the formability and the HAZ hardness change in the laser welding was evaluated. Melt-run welding with a laser-welding machine was carried out on high strength steel sheets with a tensile strength of 980MPa. To evaluate the formability of TBs, the Erichsen test was examined. The height at rupture and the rupture morphology of the TBs were investigated. As a result, the width of the weld metal and the HAZ narrowed with the increase in the welding speed, which led to an improvement in the formability evaluated by the Erichsen test. In the case of the same width of the weld metal, the formability with the Erichsen test was found to deteriorate due to the HAZ softening. CAE analysis confirmed that certain amounts of strain were locally concentrated on the HAZ softening area, which may cause formability deterioration in the Erichsen test.


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    Title :

    Effect of HAZ softening on the Erichsen value of tailored blanks


    Additional title:

    Einfluss einer Plastifizierung der Wärmeeinflusszone auf den Erichsen-Wert von maßgefertigten Blechzuschnitten


    Contributors:


    Publication date :

    2006


    Size :

    6 Seiten, 5 Bilder, 1 Tabelle, 4 Quellen


    Type of media :

    Conference paper


    Type of material :

    Storage medium


    Language :

    English




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