Microstructure And Mechanical Properties Of Aluminum Brass Subjected To The Magnetic Cryogenic Treatment

Copper and copper alloy is one of the earliest used metals by humans,and also is the indispensable important resources in the development of national economy.Al-brass can be used to make large worm and clamping screws and nuts which work under the heavy load conditions.So the harsh use conditions ask al-brass need good mechanical properties and mechanical properties.In addition to the traditional alloy strengthening method,the cryogenic treatment,magnetic field and other physical fields on the material of the modification research is getting more and more attention in the field of material preparation.In this paper,the al-brass will respectively after cryogenic treatment,pulse magnetic treatment after cryogenic treatment and static magnetic field cryogenic treatment.After these different treatment mentioned above,we will detect the mechanical properties and microstructure of al-brass samples under different processing conditions,which must need the help of electronic universal testing machine,micro-hardness tester,scanning electron microscope,metallographic microscope,X-ray diffraction,DSC analyzer and other modern detection equipment.What will be done is to explore the influence of al-brass’ s mechanical properties and microstructure after cryogenic and magnetic treatment.The main research results have been summarized as the following four aspects.(1)The results of cryogenic treatment show that: Cryogenic treatment leads to increase the crystal and the number of grain boundaries.So,on the one hand,the small angle boundaries were increased;On the other hand,the grain boundaries,dislocations,and precipitated phases interact with each other.This will improve the stability of material organization greatly.Therefore,the cryogenic treatment can improve the tensile properties and micro-hardness of aluminum brass.Among them,the tensile properties and micro-hardness of DCT24(Deep Cryogenic Treatment 24 hours)is 592 MPa and 5.6% respectively which is increased by 4.5% and 19% respectively than the original sample.And the micro-hardness is 285.8 HV,which is increased by 21.2% than the initial sample.There are phase change in the process of cryogenic treatment,such as α→β and γ→β,but no new phase generated.(2)The results of cryogenic pulse magnetic field treatment show that: Pulse magnetic field after cryogenic treatment 24 hours can’t improve the tensile strength and elongation,but cause the micro-hardness of sample DCT24 decreased obviously.And when the pulse number is the same,a lower magnetic condition corresponds to a smaller hardness.Especially,N=180,B =0.5T,the hardness of al-brass is only 255.6HV which is the lowest,and is down 10.5% from DCT24,but also increased by 7.2% than initial sample.(3)The results of static magnetic deep cryogenic treatment show that: Under the 0.3T static magnetic deep cryogenic treatment,the relative content of α in MDCT(magnetic deep cryogenic treatment samples)is increased by 7.4%~50% than DCT samples;and the relative content of γ is reduced by 13.3% ~ 29.4%.The tensile strength and elongation of MDCT samples is higher than DCT samples which is with the same time under cryogenic treatment.When T=24h,the mechanical properties of MDCT 24 is the highest,the tensile strength is 602.5 MPa and the elongation is 7.2%,which increased by 6.4% and 53.2% respectively than the initial sample,and increased by 3.1% and 28.6% respectively than DCT24.The main reason is that the MDCT samples with higher dislocation density than DCT samples,so the MCDT samples are with better tensile properties.And the soft α-phase increased,the hard and brittle γ-phase decreased,which also caused the micro-hardness declined.(4)Although cryogenic treatment or magnetic field coupling of cryogenic treatment did not cause the al-brass grains oriented toward a crystal direction,but the cryogenic and magnetic coupling process effectively caused the al-brass’ s α-phase grain orientation changes.Whit the increase of cryogenic time,the orientation index of β-phase(110)crystal plane increased gradually,that is to say,cryogenic treatment cause the small and crystal grains has gathered trend in the direction of(110)crystal plane.But,magnetic field changed this result.The Small and crystal grains which(110)crystal plane perpendicular to magnetic field direction deflected around the magnetization axis.That eventually lead to the Angle between(110)crystal plane and magnetic field direction is reduced,and the Angle between(211),(200)crystal plane and the direction of the magnetic field tends to 90 °.