Effect Of Heat Treatment And Cold Rolling On Si Precipitation And Grain Refinement In Al-1%Si Alloy

Strength and ductility are two of the most important mechanical properties of most materials.The mechanical properties of the material can be significantly improved by effective strengthening mechanisms.In general,there are many ways to improve the performance of metal materials,but the widely used ones are severe plastic deformation methods and reasonable heat treatment processes.However,the ultrafine-grained pure metal prepared by the large plastic deformation method can enhance the strength and refine the crystal grains,but the recovery effect is often accompanied by the recovery process,and the promotion of the second phase precipitation by a reasonable heat treatment process can significantly improve the heat of the material.The reasonable second phase precipitation can significantly improve the thermal stability of the material and inhibit the recovery process.Therefore,the optimization of heat treatment and deformation to achieve particle dispersion and grain refinement is of great significance for obtaining materials with excellent properties.In this paper,the material used in this experimental study is Al-1%Si alloy which was cast by melting high purity Al and Si.In order to study the effects of heat treatment and cold rolling on Si precipitation and grain refinement in Al-1%Si alloy.The fine-grained materials were prepared by room temperature rolling,low-temperature rolling,and introducing of aging heat treatment before/after rolling at room temperature;in addition,the heat treatment of the coarse-grained Al-1% Si sample was performed by direct current aging and conventional aging.The Si precipitation and grain refinement of Al-1%Si samples prepared by different methods were studied by transmission electron microscopy(TEM).The effects of Si precipitation and grain refinement on the properties of the samples were analyzed by tensile test performance.The main results are as follows 1.The temperature during the rolling process significantly affects the precipitation of thesecond phase Si particles.The sample prepared by cold rolling at room temperaturehas more finely dispersed Si particles.On the contrary,almost no second phase Siparticles are precipitated in the cryo-cold rolled sample.The thermal effect of ordinarycold rolling is beneficial to promote the precipitation of Si particles,while the lowtemperature during cryo-rolling inhibits the precipitation process of the Si particles.2.The grains prepared by the heat treatment and the cold rolling process are remarkablyrefined,the uniformity of the structure is high,and no obvious recovery process occurs.This is related to the dispersion of Si particles in the matrix,which inhibits the dynamicrecovery of the rolling process and plays a good role in stabilizing the deformationstructure.The ultrafine grained material after severe plastic deformation contains atypical layered structure,and the presence of these interfaces divides the material intocell subgrains.3.The strength of the material increases obviously after rolling,and the strength of thesample rolled at room temperature is higher than that of the cryo-rolled sample.Thetensile strength of the sample rolled at room temperature reaches 277 MPa and theelongation is 8.7%.The tensile strength was 258 MPa and the elongation was 7.8%.Because of the fine grain strengthening and work hardening that will occur during thecold rolling process,the material will be significantly strengthened.In addition,lowtemperature rolling inhibits the precipitation of second phase Si particles,resulting inlower material properties.4.Aging treatment before and after rolling reduces the strength of the material butincreases its ductility.Since the precipitation of the second phase is inhibited beforerolling,the aging after cold rolling promotes the precipitation of Si particles butreduces the dislocation density inside the material,which in turn reduces the workhardening effect.The second phase particles precipitated after aging after rolling cansignificantly improve the plasticity of the material.5.Direct current aging can accelerate the precipitation of the second phase Si particles.This is mainly because,in addition to the Joule heating effect,the current also hasvarious non-thermal effects,which can reduce the activation free energy of the phasetransition process and simultaneously increase the atomic diffusion flux,therebycausing the atomic diffusion rate to increase significantly and the second phaseprecipitation process to be significantly accelerated.