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Aluminum alloy 7050 is known for its superior mechanical properties, and thus finds its application in aerospace industry. Vertical direct-chill (DC) casting process is typically employed for producing such an alloy. Despite its advantages, AA7050 is considered as a "hard-to-cast" alloy because of its propensity to cold cracking. This type of cracks occurs catastrophically and is difficult to predict. Previous research suggested that such a crack could be initiated by undeveloped hot tears (microscopic hot tear) formed during the DC casting process if they reach a certain critical size. However, validation of such a hypothesis has not been done yet. Therefore, a method to produce a hot tear with a controlled size is needed as part of the verification studies. In the current study, we demonstrate a method that has a potential to control the size of the created hot tear in a small-scale solidification process. We found that by changing two variables, cooling rate and displacement compensation rate, the size of the hot tear during solidification can be modified in a controlled way. An X-ray microtomography characterization technique is utilized to quantify the created hot tear. We suggest that feeding and strain rate during DC casting are more important compared with the exerted force on the sample for the formation of a hot tear. In addition, we show that there are four different domains of hot-tear development in the explored experimental window-compression, microscopic hot tear, macroscopic hot tear, and failure. The samples produced in the current study will be used for subsequent experiments that simulate cold-cracking conditions to confirm the earlier proposed model. This research was carried out within the Materials innovation institute (www.m2i.nl) research framework, project no. M42.5.09340.

The invention relates to a method for removing a part from a mold and to a machine for molding said part, which is in particular made of a material having a glass-transition temperature and a melting temperature that is higher than the glass-transition temperature, and which is shaped in the cavity of a mold including at least two mold portions (3, 4) defining said shaping cavity (5) therebetween, wherein the mold is at a temperature between said glass-transition temperature and said melting temperature, and wherein the method comprises: opening the mold by spacing apart said mold portions (3, 4); locally spraying a cooling gas toward the part remaining in a portion of the mold using at least one nozzle (9); and, after a predetermined time period following the start of spraying the gas, ejecting the part from said portion of the mold, the time period being such that the part reaches a temperature that is lower than the glass-transition temperature thereof.