Abstract
The main reason for the use of returnable material, or recycled alloys, is a cost reduction while maintaining the final properties of the casting. The casting resulting quality is directly related to the correct ratio of commercial grade alloy and alloy made by remelting the returnable material in the batch. The casting quality is also affected by the purity of the secondary raw materials used, the shape complexity and the use of the casting itself. The presented article focuses on the effect of increasing the returnable material content in the batch on the hot tearing susceptibility of AlSi9Cu3 alloy. Hot tears are a complex phenomenon that combines metallurgical and thermo-mechanical interactions of the cast metal. Hot tearing susceptibility was evaluated on the basis of quantitative (HTS—hot tearing susceptibility index) and qualitative evaluation. The negative effect of returnable material in the batch was already manifested at a 20% content in the batch. The critical proportion of the returnable alloy in the batch can be stated as 50%. The alloy with a 50% returnable material content manifested insufficient results of the HTS index and qualitative evaluation, which means increased sensitivity to tearing. The negative effect of returnable material and the increased sensitivity were also confirmed in the evaluation of the fracture surface and hot tear profile. The microstructure of alloys with 50% and higher proportion of returnable material was characterized by a higher amount of iron phases (mainly Al5FeSi), whose sharp ends acted as critical regions of hot tearing and subsequent hot tear propagation, which had a major impact on the increase in hot tearing susceptibility.
Highlights
At present, we can talk about almost 100% recycling of all aluminum products
Quantitative Evaluation—Hot Tearing Index (HTI). It can be seen from the results shown in the graph for HTI1 (2) (Figure 3) that the reference alloy consisting only of the commercial grade AlSi9Cu3 alloy reached an HTI1 value of 0.43, which means a minimum susceptibility to hot tearing
In the case of alloys consisting of a major proportion of returnable material, the resulting hot tearing susceptibility” (HTS) values shifted to a slight rate of hot tearing susceptibility
Summary
We can talk about almost 100% recycling of all aluminum products. The recycling process continues the life of aluminum and its alloys. The recycling process as well as the replacement of primary alloys with remelted returnable material allows foundries to be more efficient in terms of raw materials and energy. For this reason, we can encounter castings made by exclusively using returnable material. For highly stressed or castings with complex geometry, it is necessary to find the ideal ratio of primary alloy and remelted returnable material in the batch, and to determine the right compromise between the quality and price of the casting [1,2,3,4,5,6]
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