PSI - Issue 33

Elvira Wahyu Arum Fanani et al. / Procedia Structural Integrity 33 (2021) 3–10 Fanani et al / Structural Integrity Procedia 00 (2019) 000–000

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advantages of cold forging are the resulting geometric accuracy, good surface finish and for near net shape products (Ishikawa et al., 2014). Meanwhile, warm forging is carried out at a temperature of 0.3-0.5 melting temperature (Tm). Jensrud and Pedersen reported the advantages of warm forging is forging load reduced without any changes in hardness of the product melting temperature (Tm). In addition, warm forming at moderate temperatures has all the benefits including good control of the microstructure and improved strength and ductility (Jensrud and Pedersen, 1998). The advantage of hot forging is that they do not cause damage to composites and reduce porosity (Nouri et al., 2020). Deformation of plastics without cracking is possible in the hot forging process because the flow stress is reduced dramatically and the work hardening does not occur too much at higher temperatures (Ajeet et al., 2015). 2.2 Based on the type of mold Aster type of mold, the forging can be classified into 2 types, namely open die forging and close die forging. In a closed die forging condition, in a warm or cold forging condition will cause the metal flow to be more uniform and the surface finish is better than an open die forging (Khemraj et al., 2018). 2.3 Based on the forging direction Along with the direction of forging, forging can be classified into unidirectional forging, bidirectional forging, and multidirectional forging (MDF). MDF is a technique in which the sample is pressed in a channel die to a fixed strain, removed, rotated by 90, reinserted in the channel die and pressed to the same strain, repeated forging in three orthogonal directions (Kapoor et al., 2013; Hussain et al., 2014;(Padap et al., 2009) Padap et al., 2009). Kavosi et al. found that with increasing the pass number of MDF will increasing the strength and dislocation density of alloy (Kavosi et al., 2014). From a study conducted by Zhu et al, it is known that MDF causes the grain structure is refined (Zhu et al., 2014). The MDF scheme is shown in Figure 1. 3. Microstructure The phenomenon that contributes to the weakening of the material due to a defect can be referred to as breakage. Some indications of a defect are cavities, micro-cracks, and shear bands (Tekkaya et al., 2015). There is a strong relationship between damage and the local volume fraction of the reinforcement proving that damage formation is accentuated in regions of particle clustering (Prangnell et al., 1996). One of the parameters to evaluate the forgeability of a material is the surface crack (Babu et al., 2015). Forging with a high reduction of up to 70% results in higher local strain and hardening of the matrix results in debonding and cracking damage (Shi et al., 2014). Crack is easy to form in the area close to the breakpoint, interface, and tip of whisker (Shi et al., 2014). After MDF is done causing additional dislocation, dislocation motion becomes more hard as dislocation density increases (Liu et al., 2020). When the forming process is carried out in hot conditions, metallurgy phenomena such as recovery, recrystallization, and grain growth will occur after the deformation process. SFD causes grain constriction and metal strengthening (Almeida et al., 2020). If deformation is carried out at high temperatures, grain growth can occur, then to reduce the energy stored by reducing grain expansion. In the research conducted by Ozer, it was found that there was a reduction in grain size in specimens subjected to secondary treatment (hot forging and hot extrusion) (Keshavamurthy et al., 2016). Manjunath et al. studied the microstructure of the specimen Al7050 alloy and it is known that as-cast alloy has an average grain size of 60 µm exhibits dendritic structure by passing the alloy for MDF two passes, the grain size is reduced to about 10 µm (Manjunath et al., 2020). The grain size of the matrix becomes small after the forging process due to recrystallization during hot forging deformation, where the thermal mismatch and dislocation is offered the energy to activate the recrystallization process (El-Sabbagh et al., 2012). In the Al-SiC Figure 1. Schematic of multi directional forging (MDF) (Hussain et al., 2014).