Effects Of Asymmetrical Rolling On Microstructures And Properties Of Aluminium And Aluminium Alloy Strip

The asymmetrical rolling has the advantages of decreasing rolling force and rolling torque and improving plate shape compared with the symmerical rolling. The conventional symmetrical 2-high cold mill was revamped into asymmetrical cold-rolling mill by replacing the connected gears. Asymmetrical rolling can be achieved by different peripheral velocities of the work rolls. By means of optical microscop and dgital microhardness tester, the effect of production process under different reduction rate and asymmetry ratio in a rolling-cycle on microstructures, properties and shapes(warp) of asymmetrically cold-rolled L2 and LF21 strip on ND (Normal Dircetion) was studied in this paper. The main conclusion is as follows:(1) Asymmetrical rolling is significantly advantageous to grain refining. Higher percentage of reduction and speed ratio could reinforce the effect of grain refinement. The average grain size was 72.8μm by asymmetrical rolling on the condition of a roller speed ratio of 1.52, a reduction rate of 10% while that is 92.3μm by symmetrical rolling on the same condition.(2) The additional shear strain, which made the deformation of asymmetrical rolling greater and metal flow faster, caused by the rightabout friction forces on the cross shear area. The additional shear strain together with the common compression can hasten the grain refining and the metal flow.(3) Asymmetrical rolling can notably weaken the basal fiber texture. In asymmetrical rolling, basal fiber was weakened when the asymmetrical ratio reached 1.32 on the condition of the reduction rate of 70%.(4) The asymmetrical rolling led to soften so that the values of average hardness fell down on the condition of a roller speed ratio of 1.52, a reduction rate of 70%.(5) The hardness distribution is asymmetry on the thickness of the whole workpieces so that it is important to coordinate the relationship betwent speed ratio and reduction to make the hardness distribution uniform.(6) The rolled strip will be bend toward the slower roll side on 10% reduction or toward faster roll side on 45% and 70% reduction. The direction of bend for asymmetrically rolled strip depends both on the force couple in cross shear area and the amounts of metallic flow.(7) The extent of warp is influenced by workpiece stuff, reduction rate and speed ratio. These parameters can be modified that the material is not curved after asymmetrical rolling.Therefore , the asymmetrical rolling, as a novel method of rolling, wil show an exciting prospect for being widely used in the aluminium rolling field.