Research On Mechanical Properties And Microscopic Mechanism Of 2024 Aluminum Alloy Stretched Under Electromagnetic Field

2024Al alloy is one of the commonly used hard aluminum alloys,which is widely utilized in industrial production.To further improve its processing methods and mechanical properties will be benefical to facilitate its application.According to the magnetoplastisity effect in 2024 aluminum alloy observed previously,it was analyzed that the improvement of plasticity was attributed to dislocations characteristic.In the view of quantum scale analysis,it was believed that magnetic fields have changed the spin state of free electrons,which were stimulated between dislocations and obstacles.By means of tensile test,Electronic Paramagnetic Resonace(EPR),X-ray diffraction(XRD)and Transimmion electron microscopy(TEM)detection,the effects of a single magnetic field,a single electric field and an electromagnetic coupling field on the tensile properties,microstructure of 2024 Al alloy and mechanism were explored.The research results are as follows:(1)The tensile test under single mangeic filed were processed with different magnetic induction intensity(B)and pulses number(N).The results show that: the mechanical properties of the samples subjected to magnetic fields function have been generally improved.On the basis of mechanical proerties,the optimal sample as B=1T and N=30 was obtained with 441 MPa tensile strength and 16.80% elongation,which were increased by 4.5% and 21.1% individually compared with those of the blank sample.The number of unpaired electrons was 4.54 times than blank sample.As for the mechanism of magnetic field,because the magnetic field energy satisfied the electron excitation conditions,which accelerated the increase of the unpaired electron concentration.The unpaired electrons came from the dislocation,alloyed phases or other dislocation pinning centers.In the presence of magnetic fields the free radicals will transfer following the sequence as singlet?transient?triplet states(that is S?S*?T).Accompanied by the transform of free radical states,the bonding between dislocations and pinning centers turned from strong to weak,which facilitated the depinning of dislocations and improvement of plasticity.It exhibited as magnetoplasticity effect in macroscopic view.(2)The tensile test under single electronic filed were processed with different current intensity(I).The results show that the mechanical properties of samples subjected to electric field function have been generally improved,and the best performance was achieved at I=0.8A.At this time,the tensile strength was 438 MPa and the elongation was 15.88%,which have been increased by 3.8% and 14.5% compared with those of the blank sample.The unpaired electronic number was 7.06 times than the blank sample.As for the action mechanism of electric field,it was regarded that the electronic wind accelerated the motion speed of dislocations and opened the entanglement between dislocations.It was helpful for dislocations to overcome the obstacle to the slipping system,thus the plasticity of the alloy was improved.The phenomenon was ascerntained as electroplasticity effect at the macroscopic level.(3)The tensile test under electromagnetic coupling field were processed with different current intensity(I)and constant B=1T,N=30.The results showed that the mechanical properties subjected to electromagnetic coupling field were further improved,and the best performance was achieved at I=2.4A.For this sample,the tensile strength was 442 MPa,the elongation was 16.95%,which have been increased by 4.7% and 22.2% in comparison to those of the blank sample.The unpaired electronic number was 3 times than the blank sample.In the presence of both magnetic and electric field,both the magnetoplasticity and electroplasticity effects occur simultaneously,which improved the comprehensive mechanical properties of 2024 aluminum alloy.(4)The mechanical properties of most samples subjected to above three physical fields have been changed.On the basis of improvement effect on mechanical properties,the coupling field was best followed by single magnetic then electric field.The polarization effect of magnetic and electric field benefited the excition of unpaired free electrons.Based on the theories of electronic wind and electron cloud,high concentration of free electrons would contribute to the improvement of plasticity.The main effect of the magnetic field was to promote the transformation of the free radical state,which accelerated the dislocation depinning.On the condition of tensile stress,the dislocations overcame the obstacles and their movement flexibility increased as well.Thereore,the dislocation density was enhanced together with more mobile dislocation.The phenomena of dislocation clusters and tangles decreased accompanied by well distribution of dislocation.The new characteristic of dislocation was beneficial to the plastic improvement.However,the electric current enhanced the dislocation movement ability only due to electronic wind,and the effect of plastic enhancement was weaker than magnetic field.On the condition of the electromagnetic coupling field,the polarizations of magnetic field and electric field have been suppressed,but the tensile performance arrived at the utmost because the combined effects of two fields on dislocation characteristicTo summary,when 2024 Al alloy was exposed to magnetic fields,electric fields and electromagnetic coupling fields,its tensile strength have been enhanced to a small extent while the elongation increased to a large extent.The synchronous improvement of strength and toughness have been achieved.The effects of electromagnetic fields lay in the excition of unpaired electrons and increase of movable dislocations and promoption of uniform distribution of dislocation,which benefited to improve the tensile strength together with the elongation.It is reasonably believed that the research thoughts in the paper are innovative and the research results are of theoretical and practical values.