Half-section welding has been proposed as a method to observe nugget growth throughout the resistance spot welding process. Some past studies used this technique as an in-situ monitoring approach to analyse the cracking behaviour during welding. However, there is a lack of understanding regarding the half-sectioned welding parameters, which critically impacts the liquid metal embrittlement cracking index. This study optimised half-sectioned welding parameters for liquid metal embrittlement crack analysis by developing process maps that compare the half-sectioned and full-section processes. It was found that the liquid metal embrittlement crack located at the weld shoulder can correlate to the temperature gradient in the heat-affected zone. This study proposes half-sectioned welding as a viable technique for liquid metal embrittlement analysis.

In automotive assembly, laser brazing (LB) is important for enabling high-precision, lightweight car body design with numerous fine details in body-in-white components [1]. To ensure the production of defect-free LB seams, there are automated nondestructive examination (NDE) techniques for real-time inspection. Interpreting real-time NDE data using artificial intelligence (AI)-powered processing systems represents a major step toward zero-defect manufacturing [2]. Using AI as a basis for quality control inspection enables replacing human decisions, allowing for quick correction of process conditions. Also, minimizing human interaction at production lines will boost efficiency in time, accuracy, and human recourse. As input/training dataset(s) are necessary to feed machine learning algorithms for AI development, the present work targeted emulating, on a laboratory scale, a broad variety of braze seam geometries and internal defects in LB joints that can occur in a manufacturing line. The main focus of the present study was to optimize the braze seam geometry and investigate conditions that manifest the braze seam imperfections, including a wavy appearance LB seam, spatter formation around the seam edge, and porosity, as important LB defects (key problem indicators). The formation of these defects will be understood with respect to variations in the process parameters, including laser power (LP), travel speed (TS), and wire feed speed (WFS).

Laser brazing (LB) offers significant advantages over other types of traditional seam joining methods: the ability to join dissimilar materials without significant melting of the substrates, reduced Zn burn-off in Zn-coated steels, and minimal heat-affected zone (HAZ) formation. However, the edge (or the tip) of laser-brazed beads can be one of the potential cracks initiations sites which results in catastrophic failure of the parts. The existing literature on LB offers no insights into the geometry and elemental segregation at the edge of the brazing bead as a result of the interaction between the laser beam and the substrate. To bridge this gap in knowledge, LB was conducted in the bead-on-plate configuration on two different types of Zn-coated hot-dip galvanized (GI) and galvannealed (GA) advanced high-strength steels (AHSS) using a Si-Bronze filler wire. LB provided an improved wettability because of the formation of a tail-like geometry at the bead edge of both coatings showing a high Zn concentration, which is opposed to what has been observed in similar studies on gas metal arc brazing (GMAB). LB had a significant effect on modifying the surface morphology of the GA-coating, which has previously not been reported in the literature. Similar Zn distribution of LB samples at the bead edge of both coatings clearly showed that the wettability of molten filler material in LB is improved relative to GMAB.

The third generation of advanced high-strength steels (3G-AHSS) has been developed to provide high strength and high ductility, which attract automakers. To protect these materials from corrosion during service, these materials are typically coated with zinc. During resistance spot welding (RSW), the zinc coating can melt, allowing it to penetrate into the grain boundaries (GBs), and lead to liquid metal embrittlement (LME) phenomena. Concerns regarding LME susceptibility have impacted the industrial application of 3G-AHSS; therefore, its mitigation has become a top focus for automakers. Several possible strategies for lowering LME severity by altering welding parameters have been proposed to mitigate LME in similar spot weld joints. However, these strategies were not tested on a dissimilar spot weld joint. Therefore, in this work, 1.4 mm gauge thickness galvanized (GI-coated) 3G-980 AHSS was joined with 0.6 mm thick Interstitial Free (IF) steel. In this work, current pulsation and ultra-short hold time were proposed to minimize LME severity. The robustness of the developed welding schedule was then tested on welds made with industrial disturbance factors such as pre-strained sheets (between 0 to 80% of 3G-980 material yield strength) and electrode misalignment (between 0° to 10° misalignment) compared to baseline parameters. In severe circumstances of disturbance factors, the resulting optimized welding schedule decreased LME cracking and showed improved resistance to LME, lowering LME severity by 41% for the extreme pre-strain condition and 27% for the extreme misalignment angle.

Zinc coatings are generally utilized for manufacturing corrosion-resistant advanced high-strength steels (AHSS). However, in new third generation AHSS (3G-AHSS), zinc from the coating may interact with the steel substrate leading to liquid metal embrittlement (LME) cracking during resistance spot welding (RSW). A critical RSW parameter that influences the LME response of the utilized 3G-AHSS is the electrode force. This study showed that the influence of electrode force on LME depended on whether or not welds experienced expulsion. When welding with low heat input, without expulsion, LME cracking severity decreased as electrode force increased. In such cases, increased force aided with heat extraction during welding, relieving the critical stresses required by LME cracking. In contrast, when welding with high heat input, resulting in expulsion, increased force elevated LME cracking. It was shown that high force increased the sudden indentation of the electrode into the substrate (electrode collapse), leading to rapid cooling of the weld shoulder. The rapid cooling increased the thermal stresses associated with the collapse event, promoting LME. This study established that the electrode force has two distinct roles on LME. When welding below the expulsion current, high force decreased LME. On the other hand, when welding above the expulsion current, more severe LME cracking was observed at high electrode force. The results from this study show that expulsion itself (excluding its association with increased heat input) is a factor contributing to LME cracking, which highlights the importance of considering the expulsion phenomenon in designing LME resistant welding schedules.