PSI - Issue 33

Rizki Dwi Ardika et al. / Procedia Structural Integrity 33 (2021) 171–180 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Han et al., 2020a). Fig. 4 shows the mechanism of porosity formation during MIG hybrid laser welding. During the heating process in MIG hybrid laser welding, the molten pool area contains a solution of hydrogen atoms. The dissolved hydrogen atom forms bubbles. The movement of hydrogen atoms is influenced by the flow behavior of the liquid metal. The cooling process causes the solubility of hydrogen to be reduced, and the hydrogen bubbles cannot escape from the molten pool of melt causing porosity. The shape of the porosity is irregular and has a large size (Kah et al., 2015).

Fig. 4. (a) Mechanism of metallurgical porosity formation during welding areas with dense metallurgical bubbles; (b) regions with aggregate bubble metallurgy (Zhao et al., 2020)

5. Environmental influence on porosity 5.1. Air temperature

Air temperature is one of the environmental parameters that affect the occurrence of porosity in a welded joint. During the welding process, porosity usually appears in the weld metal area due to the high solubility of hydrogen in aluminum at the aluminum melting temperature. The increase in air temperature causes the solubility of hydrogen when the aluminum is melted. In welding, melting occurs, which causes hydrogen gas to be trapped on the weld metal and results in porosity (Mathers, 2002). Welding temperature affects the welding results, especially in the compaction and cooling processes (Vishnyakov et al., 2018). Erratic air temperature results in poor welding. This causes the welding room temperature to be controlled in order to produce a good weld. Welding environments where the temperature is too high causes brittleness and affects the weld joint's resulting strength (Congcong Zhu et al., 2019). 5.2. Humidity Environmental parameters that affect the presence of porosity are air humidity. Moisture plays an important role in the formation of hydrogen-induced porosity in welded joints. Porosity causes a reduction in strength in the weld joint. The content of diffused H ions increases with increasing water vapor pressure in the air. Therefore, increased humidity affects the formation of high porosity. When humidity is higher, the weld microstructure's grain becomes coarser, and the size of the porosity increases in the fusion zone and the HAZ (Korenberg et al., 2004). Gou et al. (2015) Conducted welding of aluminum alloys by providing different humidity variation parameters of 50%, 70%, and 90%. Welded joints with 90% humidity conditions produce high porosity. In comparison, welded joints with a condition of 70% have a maximum diameter and area of porosity and a humidity condition of 50% at the weld joint results in low porosity values. Hence, the increased porosity quantity is due to increased humidity (Gou et al., 2015).