In the development of modern welded structures with longer life-time and/or higher load-carrying ability, fatigue properties are becoming more and more important. A lot of researches have been done to investigate which factors can elongate the fatigue life of weldments. Cold lap defects, were found to be important initiation sites of the fatigue failure in 1990s. In the ISO standard, cold lap is referred to as a type of micro-lack of fusion. Previous study found that most of the cold laps in GMAW process are formed in spatters. In this paper the interface of spatter/base metal was cut, polished and investigated by conventional metallographic methods. The aim is to reveal the influence of temperature on cold lap formation. In the experiments, different pre-heating temperatures of the parent plate were used in tandem GMAW. Results showed linear empirical relationship between the temperature of the parent plate and the amount of lack of fusion in the spatter/base metal interface.

Tandem gas metal arc welding (tandem GMAW) is, as a high productivity welding method of manufacturing process, utilized broadly in modern Swedish industry. Spatter is more or less an inevitable flaw in GMAW, especially for the high efficiency processes. Recently, spatter was found as a potential source of cold laps, which negatively influences fatigue life. The main objectives of this paper are to investigate the spatter/base metal interface and identify the primary factors for formation of cold laps.

Tandem GMAW was performed in a sealed chamber filled with either pure argon or pure dioxide. Cross sections of spatter and base metal were prepared and evaluated by Light optical microscopy and Scanning Electron Microscopy (SEM) with an attached Energy Dispersive Spectroscope (EDS).

Mn-Si oxides were found to enhance the lack of fusion occurrence in the spatter/base metal. The oxide of Mn and Si mostly came from oxidation of the droplets in the welding process. Spatter diameter and spatter distance was evaluated with respect to lack of fusion in spatter/base metal interface for welds using pure Ar shielding gas. From this it was concluded that temperature is another important factor for lack of fusion formation in the spatter/base metal interface.

The connection between the formation of cold laps and the presence of Mn‐Si oxides was studied. The underlying purpose is to understand the fundamental mechanisms of cold lap formation and to avoid it. Tandem gas metal arc welding (GMAW) was used to produce welded specimens in two different shielding gases (pure Ar and pure CO₂) with base metal S355 MC (EN-10149-2) and wire G3Si1 (EN ISO 14341-A). Cross-sections of welds in the cold lap location were evaluated by light optical microscopy and scanning electron microscopy combined with energy dispersive spectroscopy. The results showed that the Mn‐Si oxides significantly enhanced cold laps formation, especially the overlap type cold lap formation. The Mn‐Si oxides originated from oxidation of the droplets. These oxides transfers to the surface of the weld pool at the weld toe, where they contributed to the formation of the cold laps.

A cold lap is defined as a type of micro-lack of fusion in ISO standard (ISO 6520-1:2007) and have been found to influence fatigue properties of welds significantly. In the present study, the main purpose was to investigate the influence of preheating temperature on cold lap formation in tandem GMAW, both with respect to dimensions and occurrence probabilities.

Three different preheating temperatures were applied and cross-sections of welds were evaluated by light optical microscopy. The results showed that the cold lap occurrence frequency is a function of base metal temperature. However, the base metal temperature does not have a significant influence on cold lap depth.

The objective of this investigation was to classify and characterize the small lack of fusion defects, called cold lap, located at the weld toe. Since the defects are very small (0.01–1.5 mm) and difficult to detect by NDT methods, a better understanding of the formation mechanism is required to be able to avoid their formation. The investigation consisted of two parts. Firstly, a study was made on the type and frequency of cold laps. Three types were identified, namely “spatter cold lap”, and “overlap cold lap” and “spatter-overlap cold lap”. No relation between type or frequency of cold laps and the welding parameters could be established. Secondly, the interface between spatter and the base material was investigated using optical and scanning electron microscopy, to better understand the cold lap formation mechanism. Manganese-silicate particles were found in the interface located in such a way that they may assist cold lap formation.