Effect of Direct Recycling Hot Press Forging Parameters on Mechanical Properties and Surface Integrity of AA7075 Aluminum Alloys

Abstract

The current practice in aluminum recycling plants is to change the waste into molten metal through the conventional recycling (CR) manufacturing process. However, the CR technique is so energy-intensive that it also poses an indirect threat to the environment. This paper presents a study on meltless direct recycling hot press forging (DR-HPF) as an alternative sustainable approach that has fewer steps with low energy consumption, as well as preventing the generation of new waste. A laboratory experiment was conducted to study the mechanical properties and surface integrity of AA7075 aluminum alloy by employing a hot press forging (HPF) process under different temperatures (380, 430, and 480 °C) and holding times (0, 60, and 120 min). It was found that as the parameter increased, there was a positive increase in ultimate tensile strength (UTS), elongation to failure (ETF), density, and microhardness. The recycled chips exhibit the best mechanical properties at the highest parameters (480 °C and 120 min), whereas the UTS = 245.62 MPa and ETF = 6.91%, while surface integrity shows that the calculated microhardness and density are 69.02 HV and 2.795 g/cm3, respectively. The UTS result shows that the highest parameters of 480 °C and 120 min are comparable with the Aerospace Specification Metals (ASM) Aluminum AA7075-O standard. This study is a guide for machinists and the manufacturing industry to increase industry sustainability, to preserve the earth for future generations.

Optimizing strength of directly recycled aluminum chip-based parts through a hybrid RSM-GA-ANN approach in sustainable hot forging

“…It also improved material flow, minimized defects, and enhanced grain bonding. These arguments are supported by experimental investigations on the mechanical performance of aluminum chip-based recycled products [ 15 , 16 , 68 ].…”

Life cycle assessment of direct recycling hot press forging of aluminium AA7075 metal matrix composite

“…The HPF process requires the application of high temperatures that are carefully controlled to prevent surpassing the melting point for an extended duration. This controlled temperature environment ensures the complete dissolution of the copper and magnesium, phase-forming nearly homogeneous solid solution [8,12].…”

“…In contrast, upon comparing the minimum-maximum parameter range (450 °C and 60 min − 550 °C and 120 min), it is evident from figure 6 that the ultimate tensile strength (UTS) exhibits a significant increase from 26.27 MPa to 349.13 MPa. As for comparison the recycled AA7075 with alumina (Al2O3), the maximum UTS peaked at 349.13 MPa (550 °C/120 min) which shows an increment of 33.04% from the value of AA7075 without the presence of alumina; 233.76 Mpa [8,19]. The increase in ultimate tensile strength (UTS) indicates that incorporating alumina reinforcement enhances the ability of metal matrix composites to serve as a viable option for recycling aluminium alloy [13].…”

“…It is known that higher strains result in smaller recrystallized grain sizes. Variations in temperature and holding time significantly influence the microstructure and mechanical properties of metal matrix composites (MMCs) such as Al-7075 [8,20] .Higher temperatures and longer holding times lead to finer grain sizes and decreased in porosity, while lower temperatures and shorter holding times result in bigger grain sizes and reduced porosity. The results from tensile tests indicate that the material's structure affects its mechanical properties.…”

“…During the pre-compacting cycle (PCC), where the plunge was repeatedly struck with 350 KN force for several cycles, the temperature and force remained constant. After turning off the heat, the plunge was maintained at maximal force to initiate the cooling phase [2,6,8].…”