Development of vehicle safety components with functional mechanical properties by innovative processes

In recent years, the automotive industry has tended to use limited energy resources more efficiently, taking into account legal emission restrictions and increasing impact safety requirements. To this purpose, the development of innovative approaches and integration into the automotive industry have become more important. The main objective in these approaches is to optimize the strength-toughness-ductility balance. Reaching this goal be followed, the first preference is to use materials with high specific strength, and the second is to develop functional vehicle components using innovative methods. In the thesis, the processes from the basic research to industrial applications have been covered in the development of lightweighted and strengthened vehicle body safety components by utilizing Press Hardening (PHP) and Friction Stir Processes (FSP). With this approaches developed in the thesis, it is shown that the initial hardness value of Usibor® 1500 sheet material (250 Hv) can be adjusted to have a desired hardness value in the range of 310 Hv-500 Hv in the functional areas. Thus, the positive effects of the functional zones on the ability to cut Usibor® 1500 sheet material under lower forces and/or improve the energy damping behavior have been determined. FSP was applied to Dual Phase (DP) 600 and Transform Induced Plasticity (TRIP) 780 which represents extensively used steels grades in the automotive industry. Effects of FSP on the mechanical, microstructural, formability and impact properties of steel sheets were investigated with experimental and numerical methods. FSP process increased initial hardness of the DP 600 and TRIP 780 steel sheets from 178 Hv and 250 Hv to 315 Hv and 490 Hv respectively. The strength of DP 600 and TRIP 780 steel sheet materials increased significantly after FSP. As-received yield strength and tensile strength of TRIP 780 sheets were significantly increased from 420 MPa and 820 MPa to 1120 MPa and 1470 MPa respectively. Similarly, strength enhancement was also achieved in FSPed DP 600 steel. Yield strength and tensile strength of the steel considerably increased from 300 MPa and 620 MPa to about 811 MPa and 1053 MPa respectively. Accompanied with these strength enhancements, an acceptable reduction in ductility of both TRIP 780 and DP 600 steels was observed after FSP. FSP induced mechanical and microstructural changes have somehow reduced the formability and impact behavior of DP 600 and TRIP 780 steels. The results obtained within the scope of the thesis show that industrially applicable practical and cost effective approaches have been developed for the design/production of vehicle body safety components which can exhibit different mechanical properties on the same part.