Investigation of different lubricant classes for aluminium warm and hot forming based on a strip drawing test

Effect of Solution Treatment on Recrystallization, Texture and Mechanical Properties of 7A65-T74 Aluminum Alloy Super-thick Hot Rolled Plate

Research on the improvement of flat-clinching jointed aluminum alloy by reshaping process

Friction during contact between metals can be very complex in pulse current-assisted forming. Based on stamping process characteristics, a reciprocating friction tester was designed to study the friction characteristics between AA7075 aluminum alloy and P20 steel under different current densities. Origin software was used to process the experimental data, and a current friction coefficient model was established for the pulse current densities. The results show that the friction coefficient of the aluminum alloy sheet decreased with the increase in the pulse current density (2–10 A/mm2). After that, the friction mechanism was determined by observing microscopic morphology and SEM: some oxide cracked on the friction surface when the current was large. Finally, finite element simulations with Abaqus software and a cylindrical case validated the constant and current friction coefficient models. The thickness distribution patterns of the fixed friction coefficient and the current coefficient model were compared with an actual cylindrical drawing part. The results indicate that the new current friction model had a better fit than the fixed one. The simulation results are consistent with the actual verification results. The maximum thinning was at the corner of the stamping die, which improved the simulation accuracy by 7.31%. This indicates the effectiveness of the pulse current friction model.

/pdf/study-on-friction-characteristics-of-aa7075-aluminum-alloy-2hdy4m48.pdf

Study on Friction Characteristics of AA7075 Aluminum Alloy under Pulse Current-Assisted Hot Stamping

Hot stamping is an important manufacturing process for sheet metal parts. However, it is easy to produce defects such as thinning and cracking in the drawing area during the stamping process. In this paper, the finite element solver ABAQUS/Explicit was used to establish the numerical model of the magnesium alloy hot-stamping process. The stamping speed (2~10 mm/s), the blank-holder force (3~7 kN), and the friction coefficient (0.12~0.18) were selected as the influencing factors. Taking the maximum thinning rate obtained through simulation as the optimization objective, the response surface methodology (RSM) was applied to optimize the influencing factors in sheet hot stamping at a forming temperature of 200 °C. The results showed that the maximum thinning rate of sheet metal was most influenced by the blank-holder force, and the interaction between the stamping speed and the blank-holder force/friction coefficient had a great influence on the maximum thinning rate. The optimal value of the maximum thinning rate of the hot-stamped sheet was 7.37%. Through the experimental verification for the hot-stamping process scheme, the maximum relative error between the simulation and the experimental results was 8.72%. This proves the accuracy of the established finite element model and the response surface model. This research provides a feasible optimization scheme for the analysis of the hot-stamping process of magnesium alloys.

/pdf/process-optimization-of-the-hot-stamping-of-az31-magnesium-3h1oynvc.pdf

Process Optimization of the Hot Stamping of AZ31 Magnesium Alloy Sheets Based on Response Surface Methodology

Aluminum alloy hot stamping technology can improve the formability of materials and obtain parts with high dimensional accuracy. Friction behavior in the hot stamping process is very important for forming quality. Accurate friction coefficient is helpful to improve the prediction accuracy of forming defects. It is hard to obtain the friction coefficient by simple experiments due to the complicated thermal–mechanical coupling and contact conditions during the hot stamping of aluminum alloys. In order to explore the effect of friction behavior on forming quality, hot stamping experiments of 7075 aluminum alloy U-shaped parts with different lubricants were carried out. The influence of different lubricants on the force–displacement curve, material inflow, surface appearance, and thickness distribution of the formed part was analyzed. The results showed that a good lubrication effect could be obtained with the molybdenum disulfide lubricant. The friction coefficient under different lubrication conditions was obtained by using the inverse problem optimization method. Compared with the experimental results, the determined friction coefficients could accurately predict the force–displacement curves and the thickness distributions of formed parts under different lubrication conditions.

Determination of Hot Stamping Friction Coefficient of 7075 Aluminum

Insufficient strength of welding spots is a common problem in the hot stamping process of ultra-high strength steel patchwork blanks (UHSSP). In this paper, the welding spots of 22MnB5 boron steel with thicknesses of 1.2 and 1.5 mm were austenitized and then air-cooled to 650–850 °C for high temperature tensile shear tests and high temperature cross-tension tests, respectively. To study the mechanical properties of the welding spots at room temperature after heat treatment, the austenitized welding spots were quenched in cold water to room temperature, and microhardness tests and microstructure observations were performed. The results indicated that compared to the original welding spots, the heat-affected softening zone disappeared after heat treatment, and the hardness values of the fusion zone, heat-affected zone and base material were basically the same, at about 500 HV. After heat treatment, the welding spots were mainly martensite. With the increase in deformation temperature, the peak loads of the tensile shear and the cross tension of the welding spots decreased. At 750 °C, the peak loads of the welding spots decreased less, energy absorption was larger, and the welding spots had the comprehensive mechanical properties of strength and ductility.

Study on the Effect of Heat Treatment on Microstructures and High Temperature Mechanical Properties of Welding Spots of Hot Stamped Ultra-High Strength Steel Patchwork Blanks

Contact solution treatment (CST) of Al–Zn–Mg–Cu alloys can shorten solution time to within 40 s in comparison with 1800 s with traditional solution treatment using a heating furnace. Heating temperature is the key factor in solution treatment. Considering the short heating time of CST, the ultra-high solution temperature over 500 °C of Al–Zn–Mg–Cu alloys was studied in this work. The effects of solution temperatures on the microstructures and the mechanical properties were investigated. The evolution of the second phases was explored and the strengthening mechanisms were also quantitatively evaluated. The results showed that solution time could be reduced to 10 s with the solution temperature of 535 °C due to the increasing dissolution rate of the second phase and the tensile strength of the aged specimen could reach 545 MPa. Precipitation strengthening was the main strengthening mechanism, accounting for 75.4% of the total strength. Over-burning of grain boundaries occurred when the solution temperature increased to 555 °C, leading to the deterioration of the strength.

https://www.mdpi.com/2075-4701/11/5/842/pdf

Mingwen Ren

Papers

Determination of Hot Stamping Friction Coefficient of 7075 Aluminum

Study on the Effect of Heat Treatment on Microstructures and High Temperature Mechanical Properties of Welding Spots of Hot Stamped Ultra-High Strength Steel Patchwork Blanks

Study on Ultra-High Temperature Contact Solution Treatment of Al–Zn–Mg–Cu Alloys