Experiments And Study On Coolant And Lubricant Of Magnesium Alloy In Rolling Process

Rolling is an effective method used to impose a large amount of plastic deformation to magnesium alloy in a form of sheet. As the plastic deformation increases at appropriate temperatures, the grains become smaller in size and the mechanical properties of the sheet are improved. Today, the vast majority of magnesium parts are produced bye rolling. However, rolling process results in poorer surface properties (especially surface quality deteriorated) and rougher surfaces because of the dry rolling. The friction which is not only a waste of resources, but will also reduce the speed of the rolling was emerged between the rolls and metal piece.Lubrication plays a significant role during the rolling of magnesium sheets. The application of lubrication can decrease rolling force and frication coefficient, at the same time, the surface quality of the rolled magnesium can also be improved. The aim of the work is to determine the appropriate coolant and lubrication of the magnesium alloy process. In the process of magnesium alloy rolling, the content and species of rolling oil with different additives can be controlled to improve the quality of magnesium alloy sheets. It was used in this experiment for rolling the same thickness magnesium alloy sheets by adopting emulsion.A deep analysis and evaluation of surface quality has been done on investigation data of this experiment. The results indicate that rolling with lubrication can reduce friction between mills and magnesium alloy and improve production efficiency. The surface roughness and quality of magnesium alloy after rolling with lubrication are also decreased at the same time. Nevertheless, comparing with no lubrication and emulsion, rolling oil can remarkably improve rolling parameters and the quality of copper plates. The results ware shown as following:(1) Emulsion is a dispersion of droplets of one liquid in another one with which it is incompletely miscible. The property and application of emulsions are markedly affected bye morphology, size and distribution of dispersed phase. Test results show that using optical microscope to observe and analyze the microstructure of emulsions directly is a fast and effective method for evaluating the stability and droplet size distribution of the emulsion. It indicates that the stability of emulsions is enhanced with the refining of oil droplets and with the increase of surfactant concentrations till10percent. Comparing with other analytical methods, this method is more direct and precise.(2) In order to determine which kind of base oil is suit for lubricant in the magnesium alloy rolling process, the DSC-TG thermal analysis was used to evaluate the oxidation stability of several different base oil such as transformer oil in grade25(T25), machine oil in grade7(M7) and polyethylene glycol600(PEG600) and their emulsion. It appears clearly that the oxidation stability of emulsions at high temperature is mainly dominated by the base oil type. We can only compare them with each other to achieve which one is the most stable at rolling temperature. The results showed that PEG600and T25are suitable for lubricant. It is necessary to say that for T25as long as emulsifier and dadecanol used at the same time can improve its stability, but for PEG600using single oleic acid can improve it marked. Test results show that DSC-TG thermal analysis is a fast and effective method for evaluating the oxidative stability of magnesium alloy in rolling process at high temperature.(3) In order to develop an effective cooling lubricant for magnesium alloy in rolling process, systematic experiments about formulation research have been conducted in this work. The main components of lubricant emulsion were determined by the comparison of some candidates of base oil, transformer oil in grade10, machine oil in grade7and polyethylene glycol600, polar oil additive, dodecanol and oleic acid and emulsifier (Span80, Tween80, SDS) in microstructure and properties, respectively. It is found that the stability of emulsions is mainly dominated by the emulsifier type and concentration. The suitable stability was obtained by using compound emulsifier of nonionic and anionic surfactants and the feasible content of emulsifier is about10percent. Dodecanol can contribute to the stability of the emulsion while the oiliness agent can improve the plate-out ability of the emulsion. The stability of emulsions using compound of nonionic and anion surfactants is much better than by using any single surfactants. The plate-out ability of the emulsion increased markedly and the facial tension of emulsion decreased significantly with the increase of surfactant concentration.(4) The lubricant and coolant ware applied to experiments on magnesium alloy rolling. Research on extreme-pressure additives which is effective for magnesium alloy rolling emulsion can play a important role in the development and application of magnesium alloy.The extreme pressure properties and friction performance of the base oils-transformer oil in grade25with these three extreme-pressure additives of zinc dialkydithiosphate. triethanolamine borate and succinimide were investigated by using four-ball test machine in this study. At the same time, the surface quality of magnesium alloy which was rolled by different lubricity were observed through Metallographic microscope.The results show that when the rolling emulsion doped with ZDDP, its extreme pressure properties and tribological properties could be improved, and the friction coefficient could be reduced. Meanwhile, the quality of magnesium alloy surface is improved obviously and edge cracks are reduced significantly.