Banca de QUALIFICAÇÃO: MATHEWS LIMA DOS SANTOS

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : MATHEWS LIMA DOS SANTOS
DATE: 25/09/2023
LOCAL: Qualificação por videoconferência
TITLE:

LIQUID METAL EMBRITTLEMENT OF ADVANCED HIGH-STRENGTH STEEL DURING ROBOTIZED WELDING APPLIED IN THE AUTOMOTIVE INDUSTRY

KEY WORDS:

liquid metal embrittlement; Dual-Phase Steel; Pulsed GMAW; Design of Experiments.

PAGES: 104
BIG AREA: Engenharias
AREA: Engenharia Mecânica
SUMMARY:

The use of advanced high strength steels (AHSS) in the automotive industry is due to the specific characteristics of these materials, such as high mechanical and impact strength, formability and recyclability. Thus, thin sheets can reduce the weight of vehicles and reduce greenhouse gas emissions, keeping vehicle safety. To avoid a decrease in mechanical properties during manufacturing processes, researchers are driven to seek to understand the issues arising from the processes of joining metals. In this context, liquid metal embrittlement (LME) is a phenomenon not yet fully understood. The hypothesis of this work is to show that hot-dip galvanized Dual-Phase 600 steels (DP 600 GI) are susceptible to LME when subjected to gas metal arc welding (GMAW) with a high restriction level and that the thickness of the coating is a relevant factor for the occurrence of LME. Therefore, this doctoral thesis aims to evaluate the behavior of the LME in DP 600 steel during robotic GMAW welding. As part of this qualifying examination, the techniques of optical and scanning electron microscopy, X-ray diffraction and X-ray fluorescence were used to as-received base metal characterization. Optimized values of the engineering settings were defined using the design of experiments (DoE) methodology for the following responses: heat input, hardness at the interface between the heat affected zone (HAZ) and the fusion zone (FZ), HAZ extension and additional mass. The results of this study demonstrated that the base metal presents a very refined microstructure, with islands of martensite dispersed in a ferritic matrix. The average thickness of the coating is 7.271 ± 1.435 µm and there is a Al layer between the base metal (rich in Fe) and the coating (rich in Zn). Difractograms indicate the absence of retained austenite and Fe-Zn intermetallics. The welded joints show a hardness peak at the HAZ/FZ interface, attributed to the possible formation of martensite in the coarse-grained HAZ; in addition, it presented a drop in hardness close to that of the base metal (subcritical HAZ) due to martensite tempering. The DoE analyzes resulted in obtaining three sets of optimized parameters for the study sequence, which will include the galvanizing of the plates to obtain different thicknesses of coating and carrying out welds with a high level of restriction.

COMMITTEE MEMBERS:
Presidente - 2154866 - TIAGO FELIPE DE ABREU SANTOS
Interno - 1052048 - GUILHERME BARBOSA LOPES JUNIOR
Externo à Instituição - MILTON SERGIO FERNANDES DE LIMA