Microstructure Evolution And Mechanical Properties Of Al-Mg-Si Alloy And Its Composites By Hot-rolling

The Al-Mg-Si alloy(so-called 6xxx series)has excellent plastic workability,corrosion resistance,and high specific strength.These features make Al-Mg-Si based alloys highly preferred in the aerospace,automotive,and industrial industries.However,forming at room temperature is limited,and high rebound is important disadvantages of this material.Therefore,research on the plastic deformation behavior of 6xxx aluminum alloy will help to improve its machinability,which is crucial in industrialization.In this work,the combination of thermoforming and heat treatment effectively solves the above problems.The microstructure and tensile properties of Al-Mg-Si alloy prepared by hot rolling-quenching(RQ)process were studied.The effects of preheating temperature on microstructure evolution and mechanical properties were investigated.The effect of the preheating temperature on the age hardening of the Al-Mg-Si alloy treated by the RQ process was compared with the conventional T6 and T8 states.The RQ process produces thin sheets with high surface quality and mechanical properties.Furthermore,it shortens the production process.According to the research results of this experiment,it is found that:(1)Compared with cold rolled sheets,RQ sheets exhibit higher elongation at similar tensile strengths.This is due to the obvious dynamic recovery during the hot rolling-quenching integrated production process,resulting in improved ductility of the RQ sheet;(2)The quenching rate of the RQ process is lower than that of water quenching,which causes dynamic precipitation during RQ,but the quenching sensitivity of the RQ sample depends on the preheating temperature.The RQ sample preheated at a higher temperature(540°C)showedsignificantshort-termagehardening,whilethelowerpreheating temperature(490°C)made the age hardening rate of the RQ sample slower and to a lesser extent;(3)Compared with the T6 and T8 samples,the RQ sample exhibited high tensile strength(370oC),improved ductility and surface quality after artificial aging for 1 h.For high-tech with special performance requirements,traditional materials such as metals,ceramics and polymers are increasingly unable to meet their development needs,and the emergence of composite materials has greatly compensated for the shortcomings of single materials.In recent years,research work on composite materials for metal substrates and ceramic reinforcements has been studied.The combustion synthesis method has been widely used because of its advantages of energy saving,fast reaction speed and high product purity.However,the sample prepared by the method is prone to pores,resulting in low material density and uneven distribution of ceramic particles,so plastic processing is required twice.The treatment further improves the density and mechanical properties of the composite.Conventional rolling has been widely used in the mass production of Al-Mg-Si alloy sheets.However,for the composite material,the plasticity is low,the formability is poor,and cracking is likely to occur during the conventional rolling process.Even if the sample is rolled by multiple passes and small reductions per pass,cracking will occur,so a new rolling process is needed to solve this problem.We have adopted a new method of lining rolling(HPR).that is,adding two hard plates on both sides of the rolled piece,then heating at the same time,and finally rolling at the same time.The liner can convert the shear force in the rolling direction into compressive stress so that the sheet sample does not crack.In this paper,the effects of rolling process and rolling deformation on microstructure and mechanical properties of TiC_p/Al-Mg-Si composites and the effects of nanoparticles on deformed microstructure were investigated.The experimental results found that:(1)The plate samples prepared by the hot-rolling process of the lining plate with preheating temperature of 540oC have good surface quality,and as the rolling deformation increases,the compactness of the structure increases,and the distribution of nano-TiC_p particles is more uniform.However,unlike the hot rolling-quenching process,due to the slower cooling during the rolling process,subsequent age hardening is not obvious,and T6 heat treatment is needed to improve the material properties;(2)After the hot rolling process of the lining,the grain of the composite matrix is finer than that of the Al-Mg-Si alloy,and still retains a certain directionality;The ratio of large-angle grain boundaries in composites is low,in which the ratios of small-angle grain boundaries and large-angle grain boundaries in alloys are 63.5%and 36.5%,respectively,while the corresponding grain boundary ratios in composites are 89.2%and 10.8%;For the degree of recrystallization,the dynamic recrystallization of the composite liner during the hot rolling process is low,and the substructure dominates,wherein the alloy contains~47.8%recrystallized grains,52%substructures and 0.2%deformation.The composite,in-situ composite containing~19.9%recrystallized grains,77.3%substructure and 2.8%residual deformed structure.In the hot rolling process,the Al-Mg-Si alloy is prone to dynamic recovery.However,since the nano TiC_p hinders the movement of dislocations,it hinders the dynamic recovery,and at the same time,the already formed subgrain boundary is pinched,thereby hindering the recrystallization process;(3)After T6 treatment,the yield strength and tensile strength of TiC_p/Al-Mg-Si composites with hot rolling reduction of 80%are significantly higher than those of Al-Mg-Si alloys,which are increased by 528.7 MPa and 571.2 MPa,respectively.In the tensile fracture,the fracture mode of the composite is mainly the peeling of the interface between the nano TiC_p and the Al.