CN111926273A

CN111926273A - Combined machining method of high-strength high-toughness H62 brass

Info

Publication number: CN111926273A
Application number: CN202010704124.3A
Authority: CN
Inventors: 陈建清; 苏业涵; 孙甲鹏; 马爱斌; 江静华; 杨东辉; 宋丹
Original assignee: Hohai University HHU
Current assignee: Hohai University HHU
Priority date: 2020-07-21
Filing date: 2020-07-21
Publication date: 2020-11-13
Anticipated expiration: 2040-07-21
Also published as: CN111926273B

Abstract

The invention discloses a combined processing method of high-strength high-toughness H62 brass, belonging to the technical field of nonferrous alloy processing. The processing method mainly applies equal channel angular pressing and subsequent heat treatment processes to commercial H62 alloy with lower strength, and can improve the toughness of the alloy by controlling the structure of the structure under the condition of not changing the shape and the size of a sample. The invention has the characteristics of high yield and simple process operation and equipment requirements, and has good industrial application prospect.

Description

Combined machining method of high-strength high-toughness H62 brass

Technical Field

The invention belongs to the technical field of nonferrous alloy processing, and particularly relates to a combined processing method of a high-strength high-toughness H62 brass alloy.

Background

The brass is a copper alloy consisting of copper and zinc, the brass consisting of copper and zinc is called as common brass, the copper content of H62 brass is 60.5-63.5%, and the brass is widely used in automobile, shipbuilding, precision machinery manufacturing industry and the like due to the high strength, high hardness, good plasticity, good cutting processability, good corrosion resistance and easy welding, and can also be used for manufacturing stressed parts produced by various deep drawing and bending processing, such as pins, rivets, gaskets, nuts, guide pipes, screens, barometer springs, radiator parts and the like. However, with the improvement of the technological level and the development of industrial technology, the comprehensive toughness of the brass is required to be higher, namely, the tensile strength of the brass is required to be improved while the excellent plasticity of the brass is maintained. The common brass contains a large amount of solid solution of zinc and copper, six phases of alpha, beta, gamma, eta and the like with a certain component range are respectively contained in a solid state, when the content of copper is 60.5-63.5%, the common brass mainly consists of alpha and beta phases, wherein the alpha phase is a solid solution taking Cu as a matrix and Zn as a solute atom, the plasticity is good, the strength is low, the beta phase is a solid solution taking a CuZn electronic compound as a matrix, the strength and the hardness are higher than those of the alpha phase, the high-temperature plasticity is better than that of the alpha phase, but the plasticity at normal temperature is different from that of the alpha phase. By improving the processing technology to adjust the state of two phases, higher strength can be obtained while maintaining the excellent toughness of the material.

The existing method for improving the strength of the copper alloy mainly comprises the following steps: solid solution strengthening, fine grain strengthening, second phase strengthening, and work hardening. The grain refinement is known as an effective means capable of simultaneously improving the strength and toughness of the material, and the realization of tissue ultra-fining by means of a large plastic deformation processing technology (SPD) to improve the performance of the metal material is gradually becoming a conventional processing means. Among the SPD technologies, Equal Channel Angular Pressing (ECAP) is known as a technology having industrial application prospect, ECAP can obtain large plastic deformation without changing the shape and size of a sample, the structure and performance of the whole sample are uniform, and the ECAP has a significant grain refining effect on pure metals, alloys, intermetallic compounds and the like.

The researchers research on the ECAP processing of pure copper, and the findings show that after the ECAP processing of 16 times, pure copper crystal grains are refined, a large amount of dislocation simultaneously appears, the material deformation mechanism is shifted from the dislocation slip of a coarse crystalline state to the grain boundary slip, and the obtained superfine crystal material has very high plastic deformation capacity and strength. Wangsheng et al, a university of Dalian transportation, have conducted preliminary studies on refining H62 brass grains by ECAP, and they conducted the highest four-pass extrusion, and found that the grains were refined to some extent with the increase of the extrusion pass, but did not reach the level of fine grains, the tensile strength and hardness were improved, and the elongation was decreased. However, the study of the H62 brass for high-pass ECAP processing has not been reported, and is worthy of further study.

Disclosure of Invention

In order to improve the tensile strength and the toughness of the commercial H62 alloy, the invention provides a combined processing method of high-strength high-toughness H62 brass, which mainly applies equal channel angular pressing and subsequent heat treatment processes to the commercial H62 alloy with lower strength, can improve the toughness of the alloy by controlling the structure of a tissue under the condition of not changing the shape and the size of a sample, and has simple operation steps and equipment requirements and easy realization.

In order to achieve the purpose, the invention adopts the following technical scheme:

a combined processing method of high-strength high-toughness H62 brass comprises the following steps:

step 1, performing equal channel angular extrusion on commercial brass alloy blocks in a die to obtain an ultrafine grained alloy material;

and 2, carrying out annealing heat treatment on the ultra-fine grain material alloy to obtain the brass alloy.

Further, prior to step 1, commercial H62 alloy bulk material was wire cut into cylindrical test pieces conforming to the tooling die.

Further, before step 1, the obtained commercial H62 alloy columnar test piece is subjected to heat preservation at 560 ℃ for 10 hours and then subjected to air cooling or water cooling homogenization treatment.

Further, in step 1, the surface of the test piece and the surface of the mold need to be uniformly coated with the solid lubricant.

Further, the solid lubricant is graphite.

Further, the equal channel angular pressing in the step 1 is performed at least for one pass.

Further, the equal channel angular pressing is 8 times.

Further, the temperature of the equal channel angular pressing was 350 ℃.

Further, in the step 2, the annealing temperature is 300 ℃, and the heat preservation time is 0.5-1 h.

Compared with other processing methods for obtaining high-strength and high-toughness materials, the processing method provided by the invention has the following advantages: the method comprises the steps of continuously carrying out ECAP extrusion on commercial H62 brass alloy, thinning H62 brass alloy grains under the condition of not changing the shape and the size of a test piece, then eliminating nonequilibrium defects such as dislocation and the like generated by ECAP extrusion through subsequent annealing treatment, simultaneously keeping the ultrafine grain structure, obviously improving the tensile strength of the alloy while keeping the better toughness of the alloy, and finally obtaining the high-strength high-toughness H62 brass alloy material. The combined processing method has simple process operation and equipment requirements, can be well combined with modern industrial production, and has good industrial application prospect.

Drawings

Fig. 1 is a metallographic structure diagram at room temperature of a commercial H62 brass alloy used in example 1.

FIG. 2 is a metallographic representation of the room temperature microstructure of a commercial H62 brass alloy used in example 1 after being held at 560 ℃ for 10 hours and then water cooled.

FIG. 3 is a room temperature metallographic structure of the H62 brass alloy after ECAP 8 pass extrusion at 350 ℃ in example 1.

FIG. 4 is a room temperature metallographic structure of the 350 ℃ ECAP 8 pass extrusion +300 ℃ 30min annealing treatment H62 brass alloy of example 1.

FIG. 5 is a room temperature metallographic structure graph of H62 brass alloy treated with ECAP 8 pass extrusion at 350 ℃ and 60min annealing at 300 ℃ in example 3;

FIG. 6 is a room temperature XRD pattern of H62 brass alloy before and after initial state, 8 passes of ECAP processing, and subsequent heat treatment in the examples.

FIG. 7 is a TEM image of an H62 brass alloy coupon after ECAP processing for 8 passes (a) and 30min annealing at 300 ℃ in example 1.

FIG. 8 is a graph of the tensile strength of samples of H62 brass alloy in the as-received state, after 8 passes of ECAP processing, and before and after subsequent heat treatment in the examples.

FIG. 9 is a graph of the hardness of samples of H62 brass alloy in the as-received state, after 8 passes of ECAP processing, and before and after subsequent heat treatments in the examples.

Detailed Description

In view of the wide application prospect and the advantages of the equal channel angular pressing processing technology in the aspect of improving the toughness of the commercial H62 brass alloy, the invention carries out detailed research around the combined process of the equal channel angular pressing and the subsequent heat treatment of the commercial H62 brass alloy and aims to improve the microstructure of the commercial H62 brass alloy so as to improve the toughness of the brass alloy.

The technical scheme of the invention is further explained by combining specific examples. The method for improving the toughness of the H62 brass alloy by combining the continuous ECAP extrusion and the subsequent annealing heat treatment is not limited to the specific example. All experimental commercial H62 brass (cu0.61zn0.38) alloy specimens were cut to size of their dies by wire cutting prior to ECAP processing and were air or water cooled homogenized after 10H holding at 560 ℃ and treated by conventional pretreatment to obtain clean, dry surfaces. Depending on the actual condition of the sample surface, the pretreatment process may select different combinations of the following steps, namely: polishing, cleaning (e.g., ultrasonic cleaning), removing oil (e.g., absolute ethanol cleaning), and applying a solid lubricant (e.g., graphite).

Example 1

Commercial H62 brass alloy was processed into 19.5mm × 19.5mm × 40mm columnar test pieces by wire cutting, and a commercial H62 brass alloy block was obtained by extrusion process, and consisted of an α phase and a β phase, in which the α phase was a solid solution with Cu as a matrix and Zn as solute atoms, and the β phase was a solid solution based on CuZn electronic compound, and the crystal grains grew into stripes, as shown in fig. 1. And then keeping the temperature of 560 ℃ for 10H, and then performing homogenization treatment by air cooling or water cooling, wherein the beta phase content of the H62 brass alloy obtained by the homogenization treatment is reduced, the grain size is increased, and the grain shape is in an equiaxial transition state from a long strip shape, as shown in figure 2.

The method comprises the steps of pretreating a test piece conventionally to obtain a clean surface, uniformly coating a solid lubricant on the surface of the test piece and the surface of a die, placing the test piece into the die preheated to 350 ℃, preserving heat for 7-10 min, applying pressure to carry out continuous 8-pass ECAP extrusion, rotating the test piece by 180 degrees between adjacent extrusion passes to improve the uniformity of an extrusion tissue, carrying out significant refinement on processed grains, distributing beta phases in a short rod shape, and simultaneously recrystallizing and separating out granular beta 'phases, wherein the beta' phases are shown in FIG. 3. After annealing treatment at 300 ℃ for 30min, the beta phase content increases, the grain size uniformity improves, and the goldenrain crystal and dislocation content increases, as shown in fig. 4.

The tensile strength of commercial H62 brass alloy is less than 400MPa, and at 350 ℃, after 8 times of ECAP extrusion, the tensile strength reaches 530MPa, the total elongation is 30.34%, and after heat treatment at 300 ℃ for 30min, the tensile strength is increased to 620MPa, the total elongation is still about 30%, and the microhardness is increased to about 160 HV.

FIG. 7 is a TEM image of a sample of H62 brass alloy after ECAP processing for 8 passes and 30min annealing at 300 ℃, and it can be seen that the morphology of the sample changes.

Example 2

Commercial H62 brass alloy was processed into 19.5mm by 40mm columnar test pieces by wire cutting, and then it was heat-insulated at 560 ℃ for 10 hours and then air-cooled or water-cooled for homogenization treatment.

The method comprises the steps of pretreating a test piece conventionally to obtain a clean surface, uniformly coating a solid lubricant on the surface of the test piece and the surface of a die, placing the test piece and the die into the die preheated to 350 ℃, preserving heat for 7-10 min, applying pressure to carry out continuous 8-pass ECAP extrusion, rotating the test piece by 180 degrees between adjacent extrusion passes to improve the uniformity of an extrusion structure, and annealing at 300 ℃ for 45min to increase the content of beta phase and improve the uniformity of crystal grains.

The tensile strength of commercial H62 brass alloy is less than 400MPa, and at 350 ℃, after 8 times of ECAP extrusion, the tensile strength reaches 530MPa, the total elongation is 30.34%, and after heat treatment at 300 ℃ for 45min, the tensile strength is increased to 617MPa, the total elongation is 26.5%, and the microhardness is increased to about 167 HV.

Example 3

The method comprises the steps of pretreating a test piece conventionally to obtain a clean surface, uniformly coating a solid lubricant on the surface of the test piece and the surface of a die, placing the test piece and the die into the die preheated to 350 ℃, preserving heat for 7-10 min, applying pressure to carry out continuous 8-pass ECAP extrusion, and rotating the test piece 180 degrees between adjacent extrusion passes to improve the uniformity of an extruded structure. After annealing treatment at 300 ℃ for 60min, the beta phase content is increased and the grain uniformity is improved, as shown in fig. 5.

The tensile strength of commercial H62 brass alloy is less than 400MPa, and at 350 ℃, after 8 times of ECAP extrusion, the tensile strength reaches 530MPa, the total elongation is 30.34%, and after heat treatment at 300 ℃ for 60min, the tensile strength is increased to 608MPa, the total elongation is 25.5%, and the microhardness is increased to about 170 HV.

In the above examples, the XRD patterns of H62 brass alloy at room temperature in the original state, after 8 passes of ECAP processing and before and after the subsequent heat treatment are shown in fig. 6, and the process of changing the α -phase and the β' -phase can be seen.

As can be seen in fig. 8, the toughness of the H62 brass alloy coupon was greatly improved after 8 passes of ECAP processing and before and after subsequent heat treatments, as compared to the as-received H62 brass alloy coupon.

As can be seen in fig. 9, the strength of the H62 brass alloy coupon was greatly improved after 8 passes of ECAP processing and before and after subsequent heat treatments, as compared to the as-received H62 brass alloy coupon.

Claims

1. A combined processing method of high-strength high-toughness H62 brass is characterized by comprising the following steps: the method comprises the following steps:

step 1, carrying out equal channel angular extrusion on a commercial H62 brass alloy block in a die to obtain an ultra-fine grain alloy material;

and 2, carrying out annealing heat treatment on the ultra-fine grain material alloy to obtain the high-strength high-toughness H62 brass alloy.

2. The method of claim 1, wherein: prior to step 1, commercial H62 flavone alloy block material was wire cut into cylindrical test pieces conforming to the tooling die.

3. The method of claim 2, wherein: before step 1, the obtained columnar test piece is subjected to heat preservation at 560 ℃ for 10 hours and then air cooling or water cooling homogenization treatment is carried out.

4. The method of claim 1, wherein: in step 1, the surface of the test piece and the surface of the die need to be uniformly coated with the solid lubricant.

5. The method of claim 4, wherein: the solid lubricant is graphite.

6. The method of claim 1, wherein: and (3) performing equal channel angular extrusion for at least one pass in the step 1.

7. The method of claim 6, wherein: the equal channel angular extrusion is 8 times.

8. The method of claim 7, wherein: the samples were rotated 180 ° between adjacent extrusion passes.

9. The method of claim 1, wherein: the temperature of the equal channel angular extrusion is 350 ℃.

10. The method of claim 1, wherein: in the step 2, the annealing temperature is 300 ℃, and the heat preservation time is 0.5-1 h.