Research On Friction Stir Welding And Surface Modification Of Thermoplastic Plastics

Thermoplastic plastics have extensive applications in the present industry because that they offer excellent physical and corrosion properties,high degree freedom of processing and design.In this thesis,the high density polyethylene(HDP E),acrylonitrile butadiene styrene(ABS)and polycarbonate(PC)were used to carry out the research of friction stir welding/processing of thermoplastic plastics.The objectives were to establish basic theory which used to join thermoplastic plastics or prepared composites via friction stir welding/processing and enriched the connotation of friction stir w elding/processing.The effects of structural feature,temperature variation,welding parameters on the welding defects and shear strength of HDPE joints were investigated.The results of real time temperature monitoring showed that the peak temperature of joint increased with the increase of the rotation speed,and the cooling speed increased with the increase of the welded speed.The surface of joints easily produced defects such as nodules,burr and flash,and the inside of joints easily produced defects such as voids,gaps and pores when selecting improper welded parameters.The DSC results showed that the crystalline content dec reased from base material to weld nugget.The SAXS results showed that the regularity of base material and weld nugget was more uniform than thermo-mechanically affected zone and heat affected zone.The shear strength of joints increased then decreased with the increase of rotation speed.When increasing welded speed or decreased plunge depth,the shear strength decreased.The ABS/PC and HDPE/ABS joints were studied to carry out the study of dissimilar thermoplastic plastics joining.The results of ABS/PC joints show that it can join the compatible thermoplastic plastics by friction stir welding when the proper welded parameters were choosed.The HDPE/ABS joint showed that it can improve forming quality and properties via adding carbon nanotubes into joints.The surface roughness of joints and the number of defects were decreased when adding carbon nanotubes.The tensile shear and hardness tests were carried out as the mechanical properties of the weld samples,and the results showed that adding the carbon nanotubes to the joint increased the shear strength,but decreased the hardness of the joint.The high-density polyethylene/multiwalled carbon nanotube modified layer was fabricated via submerged friction stir processing.The effect of processing parameter and multiwalled carbon nanotubes on morphology and properties of modified layer was studied.The results showed that the surface of modified layer was smooth and defect-free.The carbon nanotube uniformly dispersed in the matrix in the form of cloud.The DSC of modified layer showed that the crystalline content decreased with the increase of multiwalled carbon nanotube.When the content of carbon nanotube was 1% and 2%,the tensile strength increased then decreased with the increase of traverse speed and rotational speed.When the content of carbon nanotube was 4%,the tensile strength decreased with the increase of traverse speed,and increased with the increase of rotational speed.The feasibility of preparing polymer/metal modified layer by submerged friction stir processing was investigated,which used HDPE as matrix and Cu as reinforcements.The results showed that the Cu powders were dispersed with the flow of matrix in the action of stir.The dispersed direction was in accordance with the flow direction of materials.The homogeneity of surface layer was more uniform than core modified layer,and the homogeneity of advancing side was more uniform than retreating side.The crystalline content of HDP E/Cu modified layer was higher than the processing sample without the Cu.The tensile strength of modified layer was lower than base material,but higher than that were processed under the same processing parameter.The microhardness of modified layer was higher than the base material and the sample without Cu.