| Mg-Li alloy is the lightest metal structure material, which has many excellent properties, such as high impact toughness, bending strength and deforming machining easily. However, the grain size is coarse and the strength is low of the cast Mg-Li alloy, which has some limit to its application. In this paper, the effect of Al-5Ti-1B and Al-3Ti-0.15C on the grain size of cast LA141 Mg-Li alloy is studied. In order to give full play to the good plastic feature of Mg-Li alloy, the extrusion-rolling processing and heat treatment methods of LA91 and LA141 alloy sheets are discussed. A surface nano-layer of LA91 alloy sheets is induced by surface mechanical processing. The effect of different treat time and heat treatment methods on the grain size of the surface nano-layer, thickness of the deformation layer, mechanical properties and corrosion properties of LA91 alloy sheets are studied. The results show that:LA141 alloys with different additions of grain refiner are successfully produced by using frequency induction furnace, protecting by argon. The results show that when the content of Al-5Ti-1B is 1.25wt%, the grain size of LA141 alloy can reduce to 640μm from 1750μm, at which dramatic grain refinement occurred. When the content of Al-3Ti-0.15C is 1.0wt%, the grain size of LA141 can reduce to 470μm from 620μm, the effect is not obvious.Thermal deformation characteristics of LA91 and LA141 are preliminarily discussed by thermal simulation testing. The stress-strain curves of LA91 and LA141 during thermal compression have the widely stable area and the peak stresses are respectively less than 40MPa and 20MPa, under the conditions of above 200℃and deformation rate of 0.01-1.0 s-1, so the two alloys could be deformed during the wide deformation rate. The stresses of LA91 at 200-250℃and LA141 at 100-150℃respectively equal to those of ZK60 and AZ31 at 350-400℃, thus the two alloys could be deformed at the lower temperature.LA91 alloy billets are prepared by extrusion and the following rolling is conducted, the microstructure evolution of the LA91 sheets is obtained. By means of cool rolling, LA91 sheets with high mechanical properties are processed which can get the strength of 180MPa and the elongation rate of 18%. By means of cross rolling, the strength improves evidently but the elongation rate has little decrease. The microstructure of the sheet consists of chain-likeαphase andβphase matrix, with the decrease of the thickness, the distance between the nearαphase decreases and the strength of the sheet increases gradually.LA141 alloy billets are prepared by extrusion. It can get the strength of 180MPa and the elongation rate of 18% under the optimal heat treatment of 200℃×1h. 0.5mm and 0.2mm thick sheets are produced by the flowing rolling. For the 0.5mm thick sheet, the best heat treatment process is 200℃×30min, which can get the strength of 144MPa, the elongation rate of 21% and the IE value of 6.3mm; For the 0.2mm thick sheet, the best heat treatment process is 200℃×20min, which can get the strength of 139MPa, the elongation rate of 13% and the IE value of 4.7mm.After surface nanocrystallization, the mechanical properties of LA91 sheets increase significantly and the anti-corrosive performance decrease gradually. For the 8# sample, the tensile strength can increase 10%, elongation can increase 53%, compared with the LA91 sheet. With the increasing of mechanical processing time, the grain size of the surface nano-layer is not obvious changed, but the thickness of the deformation layer has increased. After annealing at 150℃×20min, the grain size, thickness tensile shrength and anti-corrosive performance of the surface nano-layer have little change, but the elongation has increased.
|
PDF Full Text Request