| Abstract |
| Al-Si coated boron steel and Zn coated DP steel plates were laser-welded to manufacture a Tailor Welded Blank (TWB) for a car body frame. Hot-stamping heat treatment (900℃, 5 min) was applied to the TWB weld, and the microstructural change and transformation mechanism were investigated in the Al-rich area near the bond line of the Al-Si coated steel side. There was Al-rich area with a single phase, Fe3(Al,Si), which was transformed to α-Fe (Ferrite) after the heat treatment. It could be explained that the Fe3(Al,Si) phase was transformed to α-Fe during heat treatment at 900℃ for 5 min and the resultant α-Fe phase was not transformed by rapid cooling. Before the heat treatment, the microstructures around the Fe3(Al,Si) phase consisted of martensite, bainite and α-Fe while they were transformed to martensite and δ-Fe after the heat treatment. Due to the heat treatment, Al was diffused to the Fe3(Al,Si) and this resulted in an increase of Al content to 0.7 wt% around the Al-rich area. If the weld was held at 900℃ for 5 min it was transformed to a mixture of austenite (γ) and δ-Fe, and only γ was transformed to the martensite by water cooling while the δ-Fe was remained unchanged. |
|
|
| Key Words |
| metals, joining, phase transformation, transmission electron microscopy, Al-segregated zone |
|
|
 |
|
