In the present work, an attempt was made to predict the temperature evolution during the extrusion of 7075 aluminium alloy by means of 3D FEM computer simulation. Results show that ram speed has a significant influence on the temperature distribution in the billet, which continuously changes throughout the process, as a result of complex heat generation and heat loss. The thermal effect results in characteristic variation of extrusion pressure. At a higher ram speed, the decrease of extrusion pressure is faster during the steady-state extrusion, due to more heat generation, less heat loss and thus more steeply decreased flow stress, as the process proceeds. The temperature inhomogeneity on the cross-section of the workpiece entering the die bearing is more pronounced when ram speed is higher. While going through the die, the extrudate undergoes a process of temperature redistribution and the temperature becomes more homogeneously distributed at the die exit. The present simulation does not render support to the general statement that the corner of the extrudate is hotter than the flat surfaces. Incipient melting is predicted to occur after a half of the billet is extruded at a ram speed as low as 1 mm/s corresponding to an extrusion speed of 0.48 m/min, if the billet contains the phases with low melting points. However, if the billet of the same alloy is in an improved metallurgical condition, no melting-related defects would be expected to occur to the extrudate running at a speed eight times faster. The results also confirm the linear relationship between the increase of the maximum temperature and logarithmic ram speed during the steady-state extrusion.

Friction plays a significant role in metal-forming operations. To optimize the deformation process, it is necessary to quantify and evaluate the behavior of the lubricants. In this study, the lubrication behavior of A5 glass lubricant was investigated. Ring compression tests were conducted at constant strain rates ranging from 0.05 to 15 s-1 and at temperatures ranging from 750 to 1000℃. At temperatures lower than 950℃, the strain rate has no obvious effect on the friction factor of A5, the most significant parameter being the temperature, an increase in the temperature decreases the friction factorm to reduce. At A5 temperatures above 950℃, the effect of strain rate becomes important, the friction factor m increases with the decrease in the strain rate.

The conventional aluminium extrusion process is run at constant ram speed, leading to quality inconsistency along the length of the extruded product and even to hot shortness as a result of continued temperature evolution. In the present work, computer simulation of the process at varying ram speed was performed in order to determine the conditions to prevent the extrudate temperature from rising excessively. To maintain the maximum workpiece temperature around 500 and 480℃ corresponding to two initial microstructural states of 7075 aluminium billets, two ram speed profiles were derived from the simulation results of a series of conventional extrusion runs. The predetermined ram speed profile commenced at a relatively high value at the beginning of an extrusion cycle and decreased exponentially with ram displacement as soon as the maximum workpiece temperature reached the target value. The simulations showed that with these ram speed profiles the continued temperature increase normally occurring during conventional extrusion could be effectively inhibited. This was verified experimentally by measuring the extrudate temperature continuously using a thermocouple in the die close to the bearing and also using a multi-wavelength pyrometer behind the die. With the predetermined ram speed profiles, the fluctuations of the maximum workpiece temperature could be controlled within a range of 10℃. The time taken to extrude each billet could be significantly shortened. In addition, the die face pressure remained stable, which would also favour the consistency of the quality of the extruded product.

The compression test has been used widely in obtailning flow stress data at hot working temperatures, in order to obtain reliable data, Uniform deformation must be ensured by having adequate lubrication tbrougbout testing, in tbis paper, the lubrication bebavior of graphite was investigated by ring compression tests of Ti-6A1-4V alloy at temperatures from 750 to 1000℃ and constant strain rates from 0.05 to 15s 1. it was found that the friction factor m increases with the increase of temperature and with the decrease of strain rate. At temperatures below 800℃, the friction factor m is less than 0.3, so that graphite can be used effectively as a luhiicant in this range of temperatm-e for compression tests.

In this paper, clad sheet bonding by cold rolling has been analyzed in depth using the stream function method and the upper bound theorem. Not only have the curvature, the thickness ratio of the rolled product and rolling force, but also the locations of the neutral points and the bond point have been obtained. It is found that at low total thickness reduction, the neutral point on the upper roll contacting the harder sheet usually more closely approaches the entrance of the roll-gap than does neutral point on the lower roll. As the thickness reduction increases, the difference gradually diminishes and even reverses. It is also found that the location of the bond point at the interface is to some extent related to the initial clad ratio. A smaller the clad ratio before rolling may bring the bond point closer to the entrance of the roll-gap, which means a longer bonded length at the interface. Based on this analysis, some means of contributing to the promotion of bond strength are proposed.