Hot Forming Quenching Research Articles

The Effect of Hot Forming–Quenching and Heat Treatment Processes on the Mechanical Properties of AA6016 Aluminum Alloy Sheets

This study explored the impact of Hot Forming–Quenching (HFQ) and heat treatment processes on the mechanical properties of AA6016 sheets. The experimental findings demonstrated that at high-temperature pre-straining (HT-PS) of 15%, the strength performance of the AA6016 sheet exhibited enhancement, with a progressive increase in both the heat treatment temperature and duration. Conversely, under HT-PS conditions of 3% and 7%, the heat treatment process exhibited a relatively modest impact on the mechanical properties of the AA6016 sheet. Differential scanning calorimetry (DSC) was employed to understand the influence of different process conditions on the precipitated phases. By comparing the precipitation peaks of the β″ phase at HT-PS of 3% and 15%, it was observed that the precipitation peak of the β″ phase decreased with an increase in HT-PS. This indicated that HT-PS promoted the precipitation of the β″ phase. In order to forecast the mechanical performance of the AA6016 sheets after applying various pre-straining and heat treatment parameters, two models were used: a backpropagation (BP) neural network and a genetic algorithm (GA)-BP neural network. These models were evaluated for their fitting and predictive capabilities. The research findings demonstrated that the GA-BP neural network model exhibited superior fitting and predictive accuracy compared to the BP neural network model.

Effect of pre-aging and precipitation behavior on mechanical properties of 7055 aluminum alloy processed by hot-forming quenching

Hot-forming Quenching (HFQ) can lead to significant changes in microstructure of high-strength aluminum alloys for car body sheet. Furthermore, through effective control, desired performance of the alloys can be achieved. Three designed processes, HFQ + Natural Aging (NA) + Simulate Baking (SB), HFQ + Pre-aging (PA) + SB and HFQ + Peak-aging (T6) were applied in this work, and the evolution of precipitated phases was systematically studied using High Resolution Transmission Electron Microscopy-Selected Area Electron Diffraction (HRTEM-SAED). The results revealed the precipitation nature of η phase in 7055 aluminum alloys is that GP zone I evolves into GP zone II, on which η’ phases directly nucleate and multiply, resulting in the transformation from η’ phases into η phases. By comparing the three processes, it is found that HFQ + PA + SB has high-density and finely distributed η’ phases, and grain boundary precipitates are small and discontinuously distributed. By adjusting the pre-aging temperature and time, it can provides a large amount of precipitation nucleation basis for the baking stage and ensure that η’ phase formation with high quantity density. The end product has a tensile strength of 660.1 MPa and a yield strength of 639.4 MPa, which is the most promising sheet material for future car body application.

Biaxial formability and microstructure of an Al-Mg-Si alloy sheet post solution heat treatment

Hot forming-quenching integrated process was developed to fabricate aluminum alloy complex-shaped components by taking advantage of the enhanced formability at the temperature close to solution temperature. But, it is very difficult to evaluate the formability under biaxial tension state and continuous cooling conditions. A measuring method was proposed to evaluate the biaxial formability by combining solution heat treatment and hot gas free bulging test. The effects of temperature and pressurizing rate on the bulging ability and thickness uniformity of an Al-Mg-Si alloy sheet were clarified. The deformation mechanism was revealed by microstructure observation. It is found that excellent formability can be obtained under the high temperature with less heat loss and rapid pressurizing conditions. The limiting strain under rapid pressurizing condition decreases from 1.13 at 500 ℃ to 0.81 at 400 ℃, being at a high strain level. Thickness uniformity can be obviously improved at a higher deformation temperature accompanied by rapid loading due to the remarkable strain-rate hardening effect. Dynamic recovery is the main restoration mechanism, resulting in numerous substructures and unchanged grain size. The obtained biaxial formability closer to actual forming condition can provide fundamental guidance for forming aluminum alloy complex-shaped component by hot forming-quenching integrated process.

Deformation and strengthening behaviors of Al–Cu–Mg alloy thick plate during hot forming-quenching integrated process

The deformation and effective die quenching are critical to ensure the final dimensional accuracy and strength of the thick-walled curved components in hot forming-quenching integrated process. The deformation behavior of an Al–Cu–Mg alloy plate during bending-quenching process was thus analyzed at different temperatures and die clearances. The strengthening behavior along thickness and radial directions was evaluated under different heating and die quenching conditions. The strengthening mechanism was revealed by microstructure observation. It is found that the smaller die clearance and higher heating temperature contribute to improve the dimensional accuracy. The water-cooled die quenching can ensure the effective quenching of a bended specimen with 25 mm in thickness, being at the strengthening level of peak aging. And, the effective quenching thickness reaches 50 mm at least. Dynamic recovery is the main restoration mechanism in the integrated process. The hardness reduces while air cooling due to the formation of coarse S precipitates with average size exceeding 750 nm. Finally, a large-size tapered thick plate component with superior dimensional accuracy was successfully fabricated under the guidance of the obtained results.

Experimental and Numerical Investigation on Strengthening Behavior of 7075 Aluminum Alloy Sheets in Hot Forming–Quenching Integrated Process

Abstract 7xxx-Series aluminum alloys have a wide application prospect in the automotive industry due to its higher strength than other series of aluminum alloy. However, little literature has been reported on the formability and strengthening behavior of 7xxx-series aluminum alloys for the structural components of body in white (BIW). In this paper, the formability and strengthening behavior of 7075-T6 were investigated systematically under hot forming–quenching (HFQ) integrated process. First, compound dies with rod-heated blank holder and water-cooled lower punch and upper die were set up for experiment. For low adhesion friction and high cooling rate, the optimum blanking temperature was determined as 400 °C. Second, forming state, thickness distribution, and temperature field were investigated through experiment and finite element simulations. A-pillar reinforcement panel was successfully manufactured based on the simulation results. The simulation data showed that the maximum thinning rate of the whole part is about 14.25%, and the maximum thickening rate is about 1.95%. Third, the formability and quench sensitivity of u7075-T6 were achieved through time–temperature–transformation (TTT) curves and continuous cooling precipitation (CCP) diagrams combined with the thermo-mechanical coupling simulation. Finally, the strengthening was measured by testing the tensile strength and Vickers hardness at different positions of formed parts after artificial aging process. The testing result showed that the strength of the formed parts after artificial aging at 120 °C for 24 h were 162.7–172.2 HV and 505–528 MPa, respectively.

Modeling mechanical properties and plastic strain for hot forming-quenching AA6061 aluminum alloy parts

The hot forming-quenching integrated process (HFQ) has proved to be an effective forming method, achieving good formability and excellent mechanical properties simultaneously for aluminum alloys parts. However, the relationship between the mechanical properties and plastic deformation in the part formed by the HFQ process remains unclear. An analytical model of mechanical properties and plastic strain for an HFQ-formed 6061 aluminum alloys part was established by curve fitting of experimental data. The mechanical properties were evaluated by tensile and micro-hardness tests, and the plastic strain distribution in the HFQ process was analyzed by an automatic strain measuring system. The tensile strength and Vickers hardness showed a linear function for the HFQ-formed 6061 aluminum alloys part, and the relationship between Vickers hardness and plastic strain also presented a linear mathematical function model. The proposed analytical model reveals the mechanical properties of the HFQ-formed 6061 aluminum alloys part quickly and accurately in a non-destructive way. Furthermore, the microstructural characteristics of the HFQ-formed aluminum alloys parts were observed by scanning electron microscopy and transmission electron microscopy to clarify the strengthening mechanism. Disperse and dense Mg2Si precipitates significantly increased with increasing plastic strain during hot forming. The results showed that the improvement in strength was mainly attributable to the increase in precipitates caused by dislocation tangle and lattice distortion after HFQ forming.

Investigation into the hot forming-quenching integrated process with cold dies for high strength aluminum alloy

The hot forming of high-strength Al alloy is an effective method to achieve the lightweight structural parts on the premise of ensuring safety. Two different hot forming routes were proposed, i.e. hot forming-quenching integrated process with cold dies+120 °C/24 h (HFQ®+120 °C/24 h) and HFQ®+pre-ageing + simulated baking (HFQ®+PA + SB) respectively. The results show that the U-shaped parts under both routes exhibited good formability without obvious surface oxidation, and the overall mechanical properties were evenly distributed. The values of UTS and YS under HFQ®+PA + SB can reach 558 MPa and 480 MPa, which are comparable to those attained under HFQ®+120 °C/24 h. The volume fraction of η' phase under HFQ®+PA + SB was found to be lower than that under HFQ®+120 °C/24 h, and the size of η was larger for the former. The quantitative assessment of strengthening contributions to YS revealed that precipitation strengthening was the major strengthening mechanism. In comparison with HFQ®+120 °C/24 h, both dislocation density and solid-solution strengthening effects were improved to some extent under HFQ®+PA + SB. The results demonstrate the feasibility of the novel HFQ®+PA + SB route for the mass production of high-strength AA7075 structural parts, due to its efficiency and good overall mechanical properties.

Feasibility study on application of hot forming quenching to patchwork blanks using two-stage refilled friction stir spot welding

The objective of this study is to apply hot forming quenching (HFQ) to patchwork blanks using two-stage refilled friction stir spot welding (TFSSW). TFSSW, which consists of two stages, is a joining method that was developed to improve the joint strength achieved with conventional friction stir spot welding (FSSW). The first stage is a conventional FSSW process, and the second stage is a process for refilling keyholes. Design of experiments was used to optimize the TFSSW process parameters. When the optimum process parameters were based on TFSSW, the joint strengths were 2.97 and 4.97 kN in the first and second stages, respectively. To compensate for the disadvantages of TFSSW, HFQ, one of hot forming processes, was applied. A hat-shape forming test was performed using a patchwork blank manufactured with optimal process parameters to determine the feasibility of applying HFQ. The HFQ hat-shaped part was sequentially heat-treated under an artificial aging (T6) condition. The hardness of the weld zone was measured to confirm the degradation in mechanical properties compared to that of the conventional forming method. After performing HFQ, the hardness of the base metal was found to be approximately 105 Hv, and the hardness curve exhibits a “W” shape. The application of HFQ to patchwork blanks using TFSSW was thus validated. To investigate the advantages obtained with the application of HFQ to patchwork blanks using TFSSW, the die surface pressure during forming was analyzed and a three-point bending test was performed; the results of this test were compared with those of the HFQ patchwork blank using conventional FSSW. The die surface pressure was lower when HFQ was applied, and the three-point bending test was higher when HFQ was applied. The results showed that applying a patchwork blank using TFSSW to HFQ improves die life and improves the strength of the forming part.

Application of hot forming quenching on patchwork blank using two-stage refilled friction stir spot welding

The purpose of this study is to apply Hot Forming Quenching (HFQ) on Patchwork Blank of AA6061 using Two-stage refilled Friction Stir Spot Welding (TFSSW). TFSSW is a developed joining method to improve joint strength of conventional Friction Stir Spot Welding (FSSW) and it consists of two stages. The first stage is a conventional FSSW process and second stage is a refilling process for refilling keyhole. The Design of Experiment (DOE) was used to optimize the TFSSW process parameters. A hat shape forming test was performed using a patchwork blank manufactured with the optimal process parameters to investigate validity of applying HFQ. Formed hat shape part was sequentially heat treated with artificial aging (T6) condition. The hardness of the weld zone was measured to confirm a drop of mechanical property in comparison with the conventional cold forming, which shows the validity of HFQ application to patchwork blank using TFSSW.

Formability and lubrication of a B-pillar in hot stamping with 6061 and 7075 aluminum alloy sheets

Abstract Aluminum alloy sheets have drawn more and more attention in recent years in the automobile industry for the purpose of weight loss and energy saving. Hot forming-quenching (HFQ) integrated process (also called hot stamping) has been developed recently for heat-treatable aluminum alloy forming to improve the formability, overcome the springback of the part. In this paper, in order to investigate the formability and lubricationof a B-pillar in hot stamping with 6061 and 7075 aluminum alloy sheets, different solution heat treatment (SHT) temperatures, SHT time and lubricants were used in the stamping experiments.The forming precision detections were also carried out after trimming. The results showed that the B-pillar wrinkled badly and cracked or even broke into pieces in cold stamping with or without lubricants.The B-pillar also cracked in hot stamping without lubricants. With the help of properlubricants, B-pillars with no crackand better surface quality could be obtained. The failure mechanismswere also explained in the present work. Besides,forming precision of most regions ranged from -1mm to 1 mm and there are still large errors in the local regions of the both ends of the B-pillar.

Improvement of Weldment Properties by Hot Forming Quenching of Friction Stir Welded TWB Sheet

The purpose of this study is to improve the mechanical properties and formability of friction stir welded tailor-welded blanks (TWBs) of Al6061 alloy with a new forming method called hot forming quenching (HFQ) in which solid-solution heat-treated aluminum sheets are formed at elevated temperature. Forming and quenching during HFQ are simultaneously performed with the forming die for the solid-solution heat-treated sheet. In this study, specimens of aluminum TWBs were prepared by friction stir welding (FSW) with a butt joint. The effectiveness of FSW joining was evaluated by observation of the macrostructure for different sheet thicknesses. In order to evaluate the formability of TWBs by HFQ, a hemisphere dome stretching test of the limit dome height achieved without specimen failure was performed with various tool temperatures. A Vickers test was also performed to measure weldment hardness as a function of position. The formability and mechanical properties of products formed by HFQ are compared with those formed by conventional forming methods, demonstrating the suitability of HFQ for sheet metal forming of friction stir welded TWBs.

Hot Forming-quenching Integrated Process with Cold-hot Dies for 2A12 Aluminum Alloy Sheet

A novel process called hot forming-quenching integrated process with cold-hot dies was proposed to improve the formability and avoid thermal distortion in solution heat treatment. In this process, the heated lower dies were used to improve the forming temperature and the cooled upper dies were utilized to accomplish quenching and reduce thermal distortion. The effects of temperatures of the hot dies ranging from 100 to 450°C on strengthening were systematically investigated. The strengths were measured by Vickers hardness test and uniaxial tensile test. It was found that the temperature of heated lower dies could be improved to 450°C to slow the temperature decrease of heated sheet besides obtaining excellent strength. The temperature of both hot dies could only be improved to 250°C. The strengthening phase was the dispersed lath-shaped S precipitate with an average cross-section of approximately 50×100nm.

Investigation on strengthening of 6A02 aluminum alloy sheet in hot forming-quenching integrated process with warm forming-dies

New manufacturing technology for light-weight structure materials has been used to meet the requirements for weight reduction and safety performance. In this paper, the hot forming-quenching integrated process of 6A02 aluminum alloy sheet at different forming-dies temperatures ranging from 50°C to 350°C was investigated. Vickers hardness test and uniaxial tensile test were carried out to reveal the strengthening behavior. Microstructure evolution was observed to clarify the strengthening mechanism with electron backscattering diffraction (EBSD), transmission electron microscopy (TEM) and scanning electron microscope (SEM) methods. Results show that the Vickers hardness and tensile strength decreased with increasing forming-dies temperature. No obvious decrease in strength appeared until the forming-dies temperature reached 250°C. The corresponding Vickers hardness was increased to 100.6 HV from original 73 HV in rolled condition, and the tensile and yield strengths were 303.8MPa and 257.1MPa, respectively. When the temperature of forming-dies rose to 350°C, the tensile and yield strengths dropped to 270.1MPa and 213.7MPa, respectively. The strengthening phase in Al matrix was the dispersed needle-shaped β″ precipitates with size about 10−50nm. Transformation of the rod-shaped β′ precipitates with 150–300nm in size at the grain boundaries and in grain interiors led to the decrease in strength. The forming-dies temperature should not be higher than 250°C for the integrated forming of 6A02 aluminum alloy sheet to obtain enough strengthening effect.

Al6061 판재성형에서 핫 포밍 ��칭의 성형성 및 기계적 특성 평가

In aluminum sheet metal forming, the conventional forming methods of T4 or T6 heat-treated sheets result in low formability and dimensional accuracy. This study suggests a new forming method for aluminum sheets called as hot forming quenching (HFQ) that solves the problems faced in the conventional method. HFQ combines the heat treatment and forming processes through the forming die during the quenching of a solid solution. To evaluate the application of HFQ to the sheet forming of aluminum, an Erichsen and V-bending test are performed in this study to measure the dimensional accuracy and formability, which are then compared with those of the conventional forming method. Furthermore, the strength and hardness of the products formed by HFQ are measured to confirm the degradation in mechanical properties compared with the conventional forming method, which shows the validity of the application of HFQ to aluminum sheet metal forming.