Influence of cold-rolling and annealing conditions on formability of aluminium alloy sheet

Using an Al-Mg-Cu alloy developed for auto body panels, strip sheets are experimentally produced by various cold-rolling and annealing procedures. Tensile and metallographic properties of the sheets and their relations are examined to attain high formability. The elongation is closely related to the grain size, and increases with the final annealing temperature. The rolling texture influences the plastic anisotropy, the Lankford value of the sheets. The comparatively high Lankford values are obtained under the condition that both the intermediate and the final annealing temperatures are higher and the reduction ratio after the intermediate annealing is smaller.     

A simple approach to plane strain extrusion with dead metal zone using upper-bound theorem

This paper treats the upper-bound approach to the problem of rigid-plastic deformation in case where the configuration of the deformation zone is previously unknown. The plane strain forward extrusion process with the so-called dead metal zone is analysed by assuming a simple velocity field. The calculations are carried out for the material with or without strain hardening or strain rate sensitivity and for various reduction ratios. The numerical results show that the region of the dead metal zone becomes smaller with the increase in the reduction ratio. The calculated punch forces agree with the experimental ones fairly well. Furthermore, it is found that the dead metal zone becomes larger with increasing the strain hardening as well as the strain rate sensitivity of the material.     

Prediction of mill load in hot strip mill rolling

It has been ascertained whether or not the model capable of predicting the stress-strain relation of plain carbon steels, previously proposed, is applicable to the estimation of mill loads in the finishing process (consisting of six mill stands) of a hot strip mill. An appreciably good agreement with the predicted and measured mill load values has been obtained in the earlier passes where the strip microstructure is regarded to have completed static recrystallization, and the predicted mill loads in the later passes have been far less than the measured load owing to the effect of the strain accumulated in the previous rolling process. Then, a simple model to predict the accumulated strain has been constructed and introduced into the calculation of mill loads. As a result, the predicted mill loads have been fairly improved over the whole passes in the finishing process.     

Berechnung über das Umformverhalten von Brammen beim Vertikalwalzen

Rechnerisches Modell aus starr-plastischen finiten Elementen zum Ermitteln des Umformverhaltens von Brammen beim Vertikalwalzen. Berechnungsbeispiel zum Ermitteln des Einflusses der Breitenabnahme, der Form der Walze, des Walzendurchmessers und der Brammenbreite auf den Walzvorgang.     

Tensile properties of a few Mg-Li-Zn alloy thin sheets

The tensile properties of experimentally produced Mg-6Li-1Zn, Mg-9.5Li-1Zn and Mg-12Li-1Zn alloy thin sheets at room temperature are investigated in this study. Uniaxial tension tests are carried out for various strain rates between 1.4 × 10^–5 and 8.3 × 10^–2 s^–1, and the microstructural and textural changes during the tests are examined. The Mg-6Li-1Zn sheet is composed mainly of the (hcp) phase and inferior to the other sheets in ductility. The (bcc) phase is dominant in the Mg-9.5Li-1Zn and Mg-12Li-1Zn sheets, and they have a considerable sensitivity to strain rate. It is observed that the grains are elongated with textural change mainly in the phase at low strain rates, and the Mg-9.5Li-1Zn and Mg-12Li-1Zn sheets have sufficiently high ductility at low strain rates. The Mg-9.5Li-1Zn sheet composed of ( + ) two phase is superior to the Mg-12Li-1Zn sheet of single phase in the tensile strength.     

Deformation process of a droplet impinging on a hot oxide-scaled surface above the Leidenfrost temperature

This paper is concerned with the collision dynamics of a water droplet impinging on a hot surface heated to above the Leidenfrost temperature, focusing upon the case where the impingement side is rough (oxide-scaled) with an oxide film. The rough surface has been artificially made by rapidly quenching as-rolled stainless steel by water spraying, after it has been heated to 1000°C in a furnace. A sequence of photographs showing the progressive stages of droplet deformation have been taken on several Weber number conditions. It has been found that the droplet configuration is not axially symmetric around the initial impact point even at an early stage immediately after collision and that the irregularity of the droplet configuration is amplified as the droplet deformation proceeds. With increasing Weber number, the irregularity has been seen to be more remarkable in the later stage and finally the droplet breaks up into some parts. Therefore, the critical Weber number to specify whether or not the droplet is disintegrated on the rough surface has been found to become small compared with the smooth surface case.     

Finite element analysis of limit strains in biaxial stretching of sheet metals allowing for ductile fracture

To predict limit strains in biaxial stretching of sheet metals, a criterion for ductile fracture is combined with the finite element simulation. The limit strains are determined by substituting the values of stress and strain obtained from the finite element simulation into the ductile fracture criterion. Material constants in the criterion are obtained from the fracture strains measured in the biaxial stretching tests. Calculations are carried out for various strain paths from balanced biaxial stretching to uniaxial tension of aluminium alloy sheets, and compared with the experimental results. The predicted limit strains are in good agreement with the measured ones not only just at the fracture site but also at outside of the fracture site. It is demonstrated that the forming limit diagrams are successfully predicted by the present approach.     

Numerical analysis of the formability of an aluminum 2024 alloy sheet and its laminates with steel sheets

A criterion for ductile fracture is applied to the formability prediction of an aluminum 2024 alloy sheet and its laminated composite sheets. Axisymmetric deep-drawing processes of the 2024 sheet and the laminates clad by mild steel sheets are simulated by the finite-element method. From the calculated distributions and histories of stress and strain, the fracture initiation site and the forming limit are predicted by means of the ductile fracture criterion. The predictions so obtained are compared with experimental observations. The results show that the fracture initiation in the 2024 sheet with no appearance of necking is successfully predicted by the present numerical approach. Furthermore, it is found that the formability of the 2024 sheet is improved by sandwiching it with the mild steel sheets.     

Finite element simulation of warm deep drawing of aluminium alloy sheet when accounting for heat conduction

The deformation behaviour and the temperature change in cylindrical deep drawing of an aluminium alloy sheet at elevated temperatures are simulated by the combination of the rigid-plastic and the heat conduction finite element methods. The comparison with the experimental results shows that the forming limits and the necking sites are successfully predicted by the simulation. It is clarified that the appropriate distribution of flow stress depending on temperature must exist in the sheet for the higher limiting drawing ratio. The numerical as well as the experimental results show that the limiting drawing ratio in the warm deep drawing increases with the die profile radius.