Hot Deformation Behavior And Microstructure Evolution Of ZL270LF Aluminum Alloy

Al-Cu alloys boast high strength,exceptional corrosion resistance,and outstanding mechanical properties,making them widely employed in aerospace,civil transportation,and construction domains.ZL270LF aluminum alloy,a member of the Al-Cu series of cast alloys,stands as one of the high-performance aluminum alloys independently developed in recent years.This alloy demonstrates excellent forgeability and has gradually found application in critical lightweight automotive structural components,although research on this alloy remains limited.The relatively high degree of alloying in ZL270LF aluminum alloy results in a narrow suitable hot processing range.During the processing stage,if the parameters are not compatible,issues such as surface cracks,adiabatic shear bands,and uneven grain distribution may arise.Consequently,it is imperative to investigate the hot deformation behavior and microstructural evolution of ZL270LF aluminum alloy.This study systematically analyzes the microstructure morphology and mechanical properties of the ZL270LF aluminum alloy.During the processing of this alloy,common issues such as surface cracks,adiabatic shear bands,and uneven grain distribution significantly limit its high-temperature workability.To obtain the desired microstructure and an appropriate hot working range,isothermal compression tests were conducted on the Gleeble-3500 thermal simulator.The rheological behavior and microstructural evolution of the ZL270LF aluminum alloy were investigated using techniques such as XRD,SEM,EBSD,and TEM,and the alloy’s dynamic recrystallization mechanism during hot deformation was analyzed.The main conclusions are as follows:（1）The main strengthening phase of ZL270LF aluminum alloy is Cu Al₂,which exists in a reticulate and vermiform pattern in the as-cast state with a tendency to aggregate.Nano-sized ternary eutectic second phase particles ofα-Al+Cu Al₂+Al₂₀Cu₂Mn₃are present within the grains,contributing to grain refinement and enhanced mechanical properties of the alloy.The fracture characteristics of as-cast ZL270LF aluminum alloy are of a brittle nature,transitioning to ductile fracture after T6 heat treatment,which results in improved tensile strength,elongation,and hardness compared to the as-cast state.（2）ZL270LF aluminum alloy exhibits a strong texture during plastic deformation at different deformation temperatures（350/400/450/500°C）with a strain rate of 0.01s^-1.At deformation temperatures of 350°C and 400°C,the main texture types are{111}<110>and{001}<110>.With the increase of deformation temperature to 450°C,{001}<100>and{110}<001>textures appear.When the temperature rises further to500°C,the{111}<110>texture weakens,and the{110}<001>texture emerges,while the{001}<110>texture exhibits a more standard position compared to lower temperatures,indicating that dynamic recrystallization occurring within the grains alters the internal texture types as the deformation temperature increases.（3）During the hot deformation process of ZL270LF aluminum alloy,its rheological stress is very sensitive to changes in strain,strain rate,and deformation temperature.In the initial stage of deformation,the rheological stress rapidly rises to its peak value.After reaching the peak,the alloy exhibits a steady-state flow behavior.In the later stage of deformation with larger strain values,the sample exhibits plastic instability,causing the true stress-true strain curve to exhibit an upward trend.（4）Through the calculation of the constitutive equation,the hot activation energy of ZL270LF aluminum alloy is determined as Q=309.05 KJ/mol.Based on the constructed two-dimensional hot working map,the optimal processing conditions for ZL270LF aluminum alloy are determined to be a temperature between 420-530℃and a strain rate of 0.01-0.1 s^-1.（5）Different hot deformation temperatures and strain rates affect the morphology of deformed grains.At lower deformation temperatures and higher strain rates,the grains are dominated by small grains with severe deformation,and the alloy grain boundaries are primarily low-angle grain boundaries.As the deformation temperature increases and the strain rate decreases,dynamic recovery and dynamic recrystallization phenomena occur in ZL270LF aluminum alloy,causing grain growth,transformation of grain boundaries to high-angle grain boundaries,and gradual homogenization of the structure.（6）There are three different dynamic recrystallization mechanisms in ZL270LF during hot deformation:discontinuous dynamic recrystallization（DDRX）,continuous dynamic recrystallization（CDRX）,and geometric dynamic recrystallization（GDRX）,with CDRX being the predominant recrystallization mechanism for ZL270LF.