Banca de DEFESA: MATHEWS LIMA DOS SANTOS

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : MATHEWS LIMA DOS SANTOS
DATE: 12/04/2024
TIME: 09:00
LOCAL: Defesa por videoconferência
TITLE:

Investigation of Weldability using the Box-Behnken Methodology and Liquid Metal Embrittlement Susceptibility of Galvanized DP 600 Steel Sheets using Robotic GMAW-Pulsed Process

KEY WORDS:

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

PAGES: 112
BIG AREA: Engenharias
AREA: Engenharia Mecânica
SUMMARY:

The use of advanced high-strength steels (AHSS) in the automotive industry is due to the characteristics of these materials, such as high mechanical and impact resistance, 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 that is not yet fully understood. The hypothesis of this work is to show that hotdip galvanized Dual-Phase 600 steels (DP 600 GI) are susceptible to LME when subjected to gas metal arc welding (GMAW) with a high level of restriction. Therefore, this doctoral thesis aims to evaluate the LME behavior in a DP 600 type AHSS during GMAW robotic welding. The as-received base metal was characterized by optical microscopy (OM) and scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray fluorescence (XRF). Optimized values of welding parameters 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 ±1 µm and there is an intermediate layer of Al 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 present a hardness peak at the HAZ/FZ interface, due to the formation of lath martensite in coarse-grained HAZ – confirmed by SEM; furthermore, they showed a drop in hardness in the subcritical HAZ due to martensite tempering. Porosities were found in samples with higher heat input due to the trapping of Zn vapour during welding. Optimized parameters were obtained, which were used to validate the proposed mathematical model. All measured responses were within the prediction interval, corroborating the reliability of the proposed model.

COMMITTEE MEMBERS:
Presidente - 2154866 - TIAGO FELIPE DE ABREU SANTOS
Interno - 2296912 - OSCAR OLIMPIO DE ARAUJO FILHO
Interno - 1132272 - SEVERINO LEOPOLDINO URTIGA FILHO
Externo à Instituição - EDWAR ANDRÉS TORRES LÓPEZ
Externo à Instituição - RODRIGO JOSE DE OLIVEIRA - UEPB