The 6xxx aluminum alloy is the first choice for automotive lightweight forgings due to its excellent performance, high strength and low weight. The production time of current aluminum alloy forging generally exceeds 10 h. To reduce the production time of traditional aluminum alloy forgings, 6082-T6 aluminum alloy is used in the forming process. The effects of different heating temperatures (200 °C, 300 °C, and 400 °C) and deformation degrees (30%, 50%, and 70%) on the deformability and properties of 6082-T6 billets have been investigated. The results show that when the heating temperature is higher than 300 °C, the compressive deformation resistance obviously decreases with increasing strength. With compression at 200 °C and 70% deformation with short heating time, the strength of the sample is close to the T6 (solution treatment and artificial aging) state. A large number of dislocations and subgrains were introduced due to the compression deformation, and their amounts decreased as the heating temperature increased. The size of the precipitated phase β′′ slightly grows under a heating temperature of 200 °C. However, when the heating temperature is higher than 300 °C, the precipitated phase gradually changes from β′′, which is optimal for the strengthening effect, to β′ and β, which offer weaker strengthening. Therefore, under a lower heating temperature of 200 °C for 5 min, a large number of dislocations are introduced with the β′′ precipitated phase, leading to higher strength with less heat treatment time.

Investigation on Compressive Formability and Microstructure Evolution of 6082-T6 Aluminum Alloy

An anisotropic constitutive model for forming of aluminum tubes under both biaxial tension and pure shear stress states

Cryogenic deformation behavior of 6061 aluminum alloy tube under biaxial tension condition

Metal bellows are widely used in piping systems, aerospace, automobile and other industries due to their favourable properties including absorption of expansion, light weight and flexibility. In this paper, the fittability was presented to evaluate the convolution shape precision of the metal bellows. By establishing a finite element model of bellows hydroforming process during the bulging and forming stages, the influence of internal pressure, axial feeding and feeding loading path on the wall thickness variation and fittability of one-convolution bellows was investigated. On that basis, the hydroforming process of multi-convolution bellows was studied, and an experiment was carried out. The results showed that with the increase in internal pressure, the wall thickness of the bellows thinned overall, and the fittability of the root zone of the bellows gradually deteriorated. Some region near the crown zone did not fit the dies well when the internal pressure is small. To improve the fittability of the bellows, the actual axial feeding should be a bit less than the theoretical axial feeding. It is of importance in developing the hydroforming technique and improving the hydroforming quality of bellows.

Influence of process parameters on thinning ratio and fittability of bellows hydroforming

Positive displacement motor is a widely used downhole power drilling tool. In order to solve the problems of short life of conventional positive displacement motors and difficulty in processing micro-sized positive displacement motors with equal wall thickness, this paper proposes to use the liquid filling and external extrusion composite forming process to process the tiny size spiral tube with equal wall thickness. Based on the tensile test of 304 stainless steel and the liquid-filled and external extrusion composite forming process, a finite element model of the 5LZ54 type equal-wall spiral tube by liquid-filled and external extrusion composite forming was established. We use the finite element method to study the composite forming of liquid-filled and externally extruded metal spiral pipes with equal wall thickness. The reasonable process parameters are that the outer diameter of the tube is 51 mm, the wall thickness of the tube is 5.5 mm, the friction coefficient is 0.125, the hydraulic pressure is 700 MPa, the extrusion speed of die is 0.167 m/s, and the hydraulic pressure loading path is path 5. The spiral tube completely fits the die. The variance of the wall thickness is 0.00846, and the wall thickness is more concentrated. The minimum wall thickness is 4.948 mm, the design wall thickness is 5 mm, the maximum wall thickness is 5.353 mm, and the average wall thickness is 5.15 mm. The maximum wall thickness error of the spiral section is 0.275 mm. The wall thickness at the convex arc is larger, and the wall thickness at the concave arc is smaller. Studies have shown that it is feasible to form a spiral tube with a small size and equal wall thickness by liquid filling and external extrusion forming process.

Liquid filling and external extrusion composite forming tiny size spiral tube with equal wall thickness

Axial hydro-forging sequence for variable-diameter tube of 6063 aluminum alloy

Analytical model for tube hydro-forging: Prediction of die closing force, wall thickness and contact stress

Analysis of warping failure in tube hydro-forging

To solve the drawbacks of thinning and poor thickness uniformity in tube hydroforming, a novel method known as axial hydro-forging sequence was developed. In this method, the deformation zones will be subjected to compression deformation throughout the hydro-forging stage to decrease the thinning and improve the thickness distribution compared with the traditional tube hydroforming. To verify the feasibility of this method, experiments and finite element simulations were designed and conducted. Subsequently, the effects of the internal pressure, friction, and reduction on thickness distribution were investigated. The results indicated that the thinning ratio can be decreased significantly by compression deformation. And the thickness of the deformation zone increases with increasing reduction. Furthermore, the thickness uniformity can be improved by a thickness “self-uniformity” in the hydro-forging stage, which was attributed to the von Mises stress distribution. It is demonstrated that the thickness distribution is related to the friction coefficient, but has little dependence on the internal pressure. Experimental and simulation results show that axial hydro-forging sequence is practicable to produce the variable-diameter tube.

Experimental and numerical investigation on axial hydro-forging sequence of 6063 aluminum alloy tube

To manufacture the large-expansion-ratio double-stepped tube without thinning, a new approach known as multistage axial hydro-forging sequence has been proposed in this study. The whole forming process is divided into five stages. Compared with traditional tube hydroforming, the thickness can be increased by axial compression deformation to reduce the thinning ratio and enhance the forming capacity of the tube in hydro-forging stage and double-stepped hydro-forging stage, respectively. The proposed multistage axial hydro-forging sequence process was implemented by experiments along with the finite element simulation to validate its feasibility. The suitable loading path to prevent defects such as wrinkle and thinning was discussed. The results showed that double-stepped tube with large expansion ratio can be produced successfully with movable dies’ design. There is no thinning in the final tube, particularly in all stepped area, and a better thickness distribution could be achieved. As a result, the proposed multistage axial hydro-forging sequence can be a feasible forming approach for the fabrication of large-expansion-ratio double-stepped tubes with high reliability.

Zhigang Fan

Papers

Axial hydro-forging sequence for variable-diameter tube of 6063 aluminum alloy

Analytical model for tube hydro-forging: Prediction of die closing force, wall thickness and contact stress

Analysis of warping failure in tube hydro-forging

Experimental and numerical investigation on axial hydro-forging sequence of 6063 aluminum alloy tube

Multistage Axial Hydro-Forging Sequence: A New Forming Approach for Manufacturing of Double-Stepped Tubes