Investigation of the influence of cryogenic‐temperature machining on ultrafine‐grained chips and machined surface quality of solution‐treated aluminum 7075 alloys

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AbstractIn this study, cryogenic‐temperature formal machining technique was used to process solution‐treated aluminum 7075 alloys, the mechanical properties, morphology, and microstructure of machined surface and produced chips are investigated. Results show machining temperature has a huge influence on chip and machined surface morphology, cryogenic‐temperature machining chips and machined surfaces possess better surface integrity, chips are continuous and smoother, and machined surfaces are flatter. In contrast, room‐temperature formal machining chips exhibit serrated cracks on their free surface and the machined surface produces more serious scaly spines phenomenon. Both cryogenic‐temperature and room‐temperature samples experience severe deformation, cryogenic‐temperature machining alumium 7075 alloys max microhardness has enhanced from 98 HV 0.1 to 174 HV 0.1, and cryogenic‐temperature samples’ microhardness is higher than corresponding room‐temperature samples’ microhardness among all machining parameters. Cryogenic‐temperature can effectively suppress dynamic recovery thus chips could store more dislocations and then possess smaller ultrafine‐grained structures, accounting for higher microhardness. Besides cryogenic‐temperature inhibits precipitation of solute cluster and second phase particles and plays a lubrication effect at tool‐chip interface, thus cryogenic‐temperature machining aluminum 7075 alloys could obtain superior machined surface quality/chip morphology to improve processability. (*: Equal contributi)