CN110987703B

CN110987703B - Quantitative identification method for free-cutting environment-friendly lead-free silicon brass with high strength and high plasticity

Info

Publication number: CN110987703B
Application number: CN201911097950.XA
Authority: CN
Inventors: 杨超; 陶鲭驰; 梁良; 丁言飞
Original assignee: Guangdong Huayi Sanitary Ware Industrial Co ltd; South China University of Technology SCUT
Current assignee: Guangdong Huayi Sanitary Ware Industrial Co ltd; South China University of Technology SCUT
Priority date: 2019-11-12
Filing date: 2019-11-12
Publication date: 2020-12-04
Anticipated expiration: 2039-11-12
Also published as: CN110987703A; JP7076060B2; JP2021076588A

Abstract

The invention discloses a quantitative identification method of free-cutting environment-friendly lead-free silicon brass with high strength and high plasticity, which comprises the steps of firstly carrying out quasi-static tensile mechanical property test to determine the quasi-static tensile yield stress sigma of silicon brass alloys with different zinc equivalent_sAnd elongation; then calculating the dynamic yield stress sigma of the cutting_d(ii) a Taking the zinc equivalent of the silicon brass alloy as an abscissa and the quasi-static tensile yield stress sigma_sElongation and cutting dynamic yield stress sigma_dFor the ordinate, the quasi-static tensile yield stress σ is plotted_sElongation and cutting dynamic yield stress sigma_dObtaining quasi-static tensile yield stress sigma along with the variation trend chart of zinc equivalent_sBetween 100MPa and 250MPa, an elongation between 40% and 15% and a dynamic yield stress sigma_dLess than quasi-static tensile yield stress sigma_sThe high-strength high-plasticity free-cutting alloy. The testing method is simple to implement and low in cost, and the high-strength high-plasticity free-cutting silicon brass alloy can be quantitatively identified.

Description

Quantitative identification method for free-cutting environment-friendly lead-free silicon brass with high strength and high plasticity

Technical Field

The invention relates to lead-free silicon brass, in particular to a quantitative identification method of free-cutting environment-friendly lead-free silicon brass with high strength and high plasticity, belonging to the field of manufacturing of environment-friendly lead-free brass alloy and parts thereof.

Background

Brass is an important engineering material and is widely applied to various fields of bathrooms, household hardware, radiators, electronic instruments, low-temperature pipelines and the like. Typically, 1-3 wt.% lead is added to brass to improve its cutting properties. Elemental lead can act as a softening point during alloy cutting, which contributes to the chip breaking and anti-sticking properties of brass. Thus, lead brass is referred to as free-cutting brass. However, lead brass is increasingly subject to environmental regulations due to the deleterious effects of lead on the environment and human health. In view of this, there is an increasing interest in the development of lead-free brasses, such as silicon brass, bismuth brass, magnesium brass and graphite brass. Among these developed lead-free brasses, silicon brass is considered as an economically and environmentally viable substitute for lead brass, because silicon element is abundant worldwide and beneficial to the environment. However, the correlation of the cutting properties of silicon brass with its mechanical properties is still unclear.

With regard to the microstructure of silicon brass, its main constituent phases are generally divided into an α phase (face-centered cubic), a β phase (body-centered cubic) and a γ phase (complex cubic). The effect of the various phase compositions on the mechanical properties of the silicon brass is well understood due to the respective crystallographic characteristics, size and content. Specifically, at room temperature, α exhibits lower microhardness and higher plasticity relative to the β phase. Thus, as the content of alpha phase in the silicon brass increases, the hardness and tensile strength thereof decrease, and the elongation thereof increases accordingly. In contrast, at high temperatures, the microhardness of the alpha phase is higher than that of the beta phase. Furthermore, the gamma phase is more brittle than the alpha and beta phases, and the presence of the gamma phase in the brass matrix will result in a decrease in its elongation. Based on the above observations, it can be concluded that under complex extreme conditions (e.g. metal cutting processes) with specific high temperature variables, accompanied by other variables, different mechanical properties of the silicon brass with respect to room temperature conditions will result.

In cutting plastic brass, chip breaking ability plays a crucial role in smooth progress of the cutting process, because continuous long chips are easily tangled and entangled. In particular, the alpha and beta phases in brass have a significant effect on the chip formation properties of brass. For example, the beta phase favors chip breakage in brass machining, while the alpha phase favors the generation of long ribbon-like chips (j.inst.met.69(1940/41) 65-79); brass with an α + β phase will result in spiral chips, whereas brass with a complete β phase is prone to produce spiral and tubular chips (j. mater. process. tech.170(2005) 441-; α + β brass has excellent chip breaking ability due to its non-uniform microstructure and moderate microhardness difference between the α and β phases (mater. sci. eng.a 723(2018) 296-305). These findings provide some useful guidance for understanding the chip breaking ability of silicon brass. However, in the above work, the chip breaking ability of brass alloys can only be qualitatively evaluated based on macroscopic chip morphology by microstructure analysis and static mechanical property testing.

However, silicon brass alloys obtained by different formulas and preparation processes are difficult to distinguish in external forms, such as low-strength high-plasticity difficult-to-cut alloy, high-strength low-plasticity difficult-to-cut alloy and high-strength high-plasticity easy-to-cut alloy, which have no substantial difference in appearance, but are extremely poor in application, the high-strength high-plasticity easy-to-cut alloy has extremely important value, and the low-strength high-plasticity difficult-to-cut alloy and the high-strength low-plasticity difficult-to-cut alloy have no good application value at present, so that how to quantitatively identify the high-strength high-plasticity easy-to-cut environment-friendly lead-free silicon brass has important significance.

Disclosure of Invention

The invention aims to overcome the defect that the chip breaking capability of silicon brass alloy is qualitatively evaluated only based on macroscopic chip morphology in the prior art, the high-strength high-plasticity free-cutting environment-friendly lead-free silicon brass is difficult to effectively identify, the chip breaking capability is regulated and controlled by correlating geometric morphological parameters and cutting dynamic mechanical properties of silicon brass alloy chips, and the high-strength high-plasticity free-cutting lead-free silicon brass quantitative identification method is established to effectively identify the high-strength high-plasticity free-cutting alloy.

Metal cutting is a highly nonlinear plastic deformation process characterized by high temperatures, high strain rates, and transients. Under such extreme dynamic conditions, the mechanical properties of the material are considered to have significantly different characteristics from the static mechanical properties at room temperature. Therefore, in order to adjust the cutting performance of silicon brass, it is more appropriate to establish a relationship between the microstructure and the dynamic performance under cutting conditions. In general, the dynamic mechanical properties are measured by the Split Hopkinson Pressure Bar technique, and the strain rate is as high as 10⁴And s. Further, from the material flow stress measured by this technique, a stress-strain model of the material under study can be determined. However, the operation process is relatively complex, skillful, cost-effective, and requires adjustment for different materialsAnd (5) integrating and verifying the corresponding stress-strain model. On the other hand, based on the cutting theory of Mechant (eng.fract.mech.76(2009) 2711-.

The method regulates and controls the chip breaking capacity by correlating geometric form parameters and cutting dynamic mechanical properties of brass chips, and is specifically characterized in that the dynamic yield stress sigma of silicon brass with different alloy components (different zinc equivalent/different microstructures) is quantitatively calculated by combining geometric characteristic quantitative parameters of the chips and cutting theory_dFrom dynamic yield stress σ_dThe component range of the silicon brass easy to break is determined along with the state of the sudden drop of the alloy zinc equivalent, and the silicon brass has the comprehensive properties of easy cutting, high strength, plasticity and the like.

The purpose of the invention is realized by the following technical scheme:

the quantitative identification method of the free-cutting environment-friendly lead-free silicon brass with high strength and high plasticity comprises the following steps:

1) quasi-static tensile yield stress sigma_sAnd elongation testing: performing quasi-static tensile mechanical property test on the silicon brass alloy rod body with the zinc equivalent of 38-49 percent to obtain a stress-strain curve, and determining the quasi-static tensile yield stress sigma of the silicon brass alloy with different zinc equivalents_sAnd elongation;

2) dynamic yield stress sigma_dAnd (3) calculating: performing a cutting test on the zinc equivalent silicon brass alloy with the zinc equivalent of between 38 and 49 percent, collecting chips, and calculating the cutting dynamic yield stress sigma when the silicon brass alloy with different zinc equivalents is cut through a cutting force model based on Mechant_d；

3) Quantitative identification of silicon brass alloy: taking the zinc equivalent of the silicon brass alloy as an abscissa and the quasi-static tensile yield stress sigma_sElongation and cutting dynamic yield stress sigma_dFor the ordinate, the quasi-static tensile yield stress σ is plotted_sElongation and cutting dynamicsYield stress sigma_dA trend graph along with the change of zinc equivalent; silicon brass alloys are classified into three types according to the trend graph:

quasi-static tensile yield stress sigma_sLess than 100MPa, elongation higher than 40% and dynamic yield stress sigma_dGreater than quasi-static tensile yield stress sigma_sThe low-strength high-plasticity difficult-to-cut alloy;

quasi-static tensile yield stress sigma_sMore than 250MPa, elongation less than 15% and dynamic yield stress sigma_dGreater than quasi-static tensile yield stress sigma_sThe high-strength low-plasticity difficult-to-cut alloy of (2);

quasi-static tensile yield stress sigma_sBetween 100MPa and 250MPa, an elongation between 40% and 15% and a dynamic yield stress sigma_dLess than quasi-static tensile yield stress sigma_sThe high-strength high-plasticity free-cutting alloy.

To further achieve the object of the present invention, preferably, the preparation method of the silicon brass alloy with different zinc equivalent in step 1) comprises the following steps: mixing Cu, Zn, Si and Al according to the following mass percent, wherein the Cu accounts for 56-66 wt.%, the Zn accounts for 33-42 wt.%, the Si accounts for 0.4-1.5 wt.%, the Al accounts for 0.2-1.5 wt.%, and the B accounts for 0.003-0.01 wt.% and the Ti accounts for 0.03-0.06 wt.%; and the zinc equivalent X% of all the components of the brass alloy is between 39 and 49%, and the microstructure is an alpha + beta phase.

Preferably, the phase composition is designed by the zinc equivalent rule, the zinc equivalent is represented by the formula

Wherein X% is the zinc equivalent; c_ZnPercentage of pure zinc added to the alloy, C_CuPercentage of pure copper, Sigma C, added to the alloy_iK_iIs the percentage content C of all other alloying elements except Cu and Zn in the alloy_iAnd its zinc equivalent coefficient K_iThe sum of the products.

Preferably, in step 2), the dynamic yield stress σ at cutting is calculated using the test protocol developed by j.g. william for cutting silicon brass alloys of different zinc equivalents_d。

Preferably, the cutting test in step 2) is performed on a CNC lathe equipped with a cutting force dynamometer, the cutting sample is a cylindrical bar, the cutting tool material is a commercial WC-8Co tool, the changed process parameter is the value of the feed rate f, which is 0.05-0.3mm/r according to the cutting parameters commonly used for brass alloys.

Preferably, the dynamic yield stress σ of cutting_dEquation derived from force balance

Is determined in which h_c,/sin phi, the length of the shear plane, h_cPhi is the cutting layer thickness and the shearing angle of the silicon brass sample; k_bIs the fracture toughness of the material, w_cIs the cutting width, F_cIs the main cutting force, F_tIs feed resistance; converting said force balance equation into

Calculating F_c/w_c-(F_t/w_c) tan phi and (h)_c/2) (tan. phi. + 1/tan. phi.); by plotting and linear fitting F_c/w_c-(F_t/w_c) tan phi and (h)_c/2) (tan phi +1/tan phi), the slope being the dynamic yield stress σ in cutting_d；

Shear angle phi of silicon brass sample

Calculation of where γ₀Is the rake angle of the cutting tool; lambda_hIs the coefficient of cutting deformation of

Determination of h_chIs the average chip thickness.

Preferably, the chip thickness h of the serrated chips_chThe equivalent value of (A) is obtained by a simplified method

Is obtained, wherein H is saw toothMaximum height of chip-like pieces, h_sIs the height of the serrations.

Preferably, the thickness h of the cutting layer_cEqual to the feed f value in the cylinder turning test.

Preferably, the cutting width w_cEqual to the back rake amount a of the cutting edge in the cylindrical turning test_p。

Preferably, in the step 3), the high-strength high-plasticity free-cutting alloy is applied to manufacturing of bathrooms, household hardware, radiators, electronic instruments and low-temperature pipelines.

Dynamic yield stress sigma of the invention_dBased on the Mechant's cutting force model, i.e., the force component acting on the shear plane in fig. 2, a test protocol developed by j.g. william was used for calculation. The chips are chips generated by brass samples collected by chip collectors arranged on lathes, and the thickness h of the chips is measured by randomly selecting 10-20 chips_chAnd (4) the related chip geometric form parameters are equal, and finally, the average value is taken to determine each chip characteristic parameter.

The dynamic yield stress sigma in the quantitative identification of the silicon brass alloy in the step 3) of the invention_dA falling zone having a value less than the quasi-static yield stress sigma_s. Dynamic yield stress sigma_dIn the descending area, the corresponding silicon brass alloy has the comprehensive properties of high strength, high plasticity, easy cutting and the like. Dynamic yield stress sigma of cutting_dDown to less than the quasi-static yield stress sigma of the material_sIn this case, it is advantageous to obtain an alloy which is free-cutting. The silicon brass alloy corresponding to the high-strength high-plasticity free-cutting area has the comprehensive properties of high strength, high plasticity, easy cutting and the like, and the zinc equivalent corresponding to the area is an alloy component area with excellent comprehensive properties; the silicon brass alloy with excellent comprehensive performance can be applied to the manufacture of bathrooms, household hardware, radiators, electronic instruments and low-temperature pipelines; while other areas have had their use more limited.

Compared with the prior art, the invention has the following advantages and beneficial effects:

1. the method quantitatively evaluates the chip breaking capacity of the silicon brass alloy material by correlating the geometric form parameters of the metal alloy chips and the dynamic mechanical properties of cutting, has the characteristics of simple implementation, low cost and the like, and overcomes the defect that a stress-strain model needs to be established in the traditional identification method considering the dynamic extreme conditions of the material cutting engineering.

2. The invention establishes a quantitative identification method for the comprehensive performance (high strength, high plasticity and easy cutting) of the silicon brass alloy, further provides a component design method for the comprehensive performance of the silicon brass alloy, and provides a powerful reference for the design of novel silicon brass alloys.

3. Cutting dynamic yield stress sigma of the invention_dDown to less than the quasi-static yield stress sigma of the material_sThe method is favorable for obtaining the free-cutting silicon brass alloy, and can be applied to the testing of the free-cutting performance and the comprehensive performance of other metal alloy materials.

Drawings

FIG. 1 is a geometric characteristic parameter characteristic diagram of a serrated chip.

FIG. 2 is a model diagram of Mechant cutting force when cutting a metal alloy.

FIG. 3 shows the cutting speed v in the example_cQuasi-static tensile yield stress sigma of silicon brass alloy with different zinc equivalent when the alloy is 90m/min_sAnd elongation, cutting dynamic yield stress sigma_dThe change trend of the zinc equivalent is shown.

Detailed Description

For a better understanding of the present invention, the present invention will be further described with reference to the following examples and drawings, but the embodiments of the present invention are not limited thereto.

Examples

(1) preparation of silicon brass alloy: the Cu, Zn, Si and Al elements are mixed according to the mass percentage of A, B, C, D, E alloy numbers shown in the table 1, 0.005 percent of B and 0.05 percent of Ti in mass percentage are added as an intermetallic compound modifier and a grain refiner, and the cylindrical rod-shaped silicon brass alloy is obtained by casting. Designing phase composition by zinc equivalent rule, zinc equivalent (X%) passing formula

Is calculated, wherein C_ZnIs the percentage content of pure zinc added to the alloy, C_CuPercentage of pure copper, Sigma C, added to the alloy_iK_iIs the percentage content C of all other alloying elements except Cu and Zn in the alloy_iAnd its zinc equivalent coefficient K_iSum of products (i represents the number of different alloying elements), K of each element_iCan be found in the handbook related to copper alloys, wherein K is the element of Si and Al _i10 and 6 respectively.

X-ray diffraction analysis shows that as the zinc equivalent increases from 39.2%, 42.7%, 45.3%, 46.9% to 48.4%, the zinc equivalent of all components of the silicon brass alloy phase composition is changed from an alpha + beta dual phase to a pure beta phase is between 39 and 49%, the microstructure takes the beta phase as a matrix, and granular or small-block alpha phase is embedded in the beta phase matrix.

(2) And (3) testing quasi-static tensile mechanical properties: according to the national standard GB/T288-2002, the quasi-static tensile mechanical property tests are respectively carried out on the prepared silicon brass alloy rod bodies with the zinc equivalent of 39.2%, 42.7%, 45.3%, 46.9% and 48.4%, the stress-strain curve is obtained, and the corresponding quasi-static tensile yield stress sigma is obtained from the tensile stress-strain curve_sAnd elongation 66MPa and 42.1%, 95MPa and 48.8%, 147MPa and 29.5%, 213MPa and 13.1%, and 257MPa and 9.5%, respectively. As shown in Table 1, Table 1 shows the elemental composition, phase content and quasi-static tensile yield stress σ of the various zinc equivalent silicon brass alloys of the examples_sAnd elongation case table. Where the compositional data was from a metal spectrometer compositional analysis and the phase composition was from an XRD test.

TABLE 1

(3) Cutting test: cutting tests were performed on a CNC lathe (CA6150i, DMTG co., China) for the prepared silicon brass alloys with zinc equivalents of 39.2%, 42.7%, 45.3%, 46.9% and 48.4%,the lathe was equipped with a cutting force dynamometer (9265-A1, Kistler Group, Swizerland) cutting a specimen into a cylindrical rod of 35X 120mm in diameter; the cutting tool material is commercial WC-8Co (Katsuka diamond tool Co., Ltd., China) tool with a rake angle gamma₀Angle of clearance α 4 °₀At 3 deg. and angle of inclination λ _s0 ° and side cutting edge angle K_r90 DEG and nose radius R_nGeometric characteristic parameters such as 1 mm. The cutting parameters in the cutting test were set as follows: cutting speed v_c90m/min, feed rate f 0.1mm/r, depth of cut a_p0.5 mm; 20 chips were collected by using a chip collector mounted on a lathe, and the average chip thickness h of silicon brass alloys of different zinc equivalent was measured by a scanning electron microscope_chMaximum height H of saw-toothed chips, height H of saw-toothed teeth_sWhen the geometrical characteristic parameters of the chips were equal, as shown in Table 2, the above CNC lathe, cutting force gauge, WC-8Co tool and cutting parameters were used, the feed rate f was changed to 0.15mm/r, cutting tests were performed on silicon brass alloys of different zinc equivalents, the chips were collected, and the average chip thickness h of the silicon brass alloys of different zinc equivalents was measured_chMaximum height H of saw-toothed chips, height H of saw-toothed teeth_sGeometric characteristic parameters of the equal chips are shown in table 2. Table 2 shows the calculation of the dynamic yield stress σ at cutting for silicon brass alloys of different zinc equivalent in examples 1 to 5_dThe required related characteristic parameters and the calculation results thereof.

TABLE 2

(4) Calculating the cutting dynamic yield stress: based on the Mechant's cutting force model, the F when different zinc equivalent silicon brass alloys are cut is calculated using the test scheme developed by J.G.William_c/w_c-(F_t/w_c) tan phi and (h)_c/2) (tan + 1/tan) the specific calculation steps and the required relevant characteristic parameters are as follows:

shear angle phi of silicon brass samples according to the geometrical characteristics of the chips

Calculation of where γ₀Is the rake angle of the cutting tool; lambda_hIs the coefficient of deformation by cutting

Is determined in which h_chThe thickness of the chip can be directly measured by observing the appearance characteristics of the chip; h is_cIs the thickness of the cutting layer, and is equal to the feed f value in the cylindrical turning test. When the serrated chips are generated, the serrated chip thickness h_chThe equivalent value of (A) can be simplified

Is obtained, where H is the maximum height of the serrated chips, H_sIs the height of the serrations as shown in figure 1. Based on the above calculations, the shear angle φ for a certain zinc equivalent silicon brass alloy at a certain cutting speed is obtained.

Based on the cutting force model of Mechant, the test protocol developed by J.G.William was applied to calculate the dynamic yield stress sigma when cutting silicon brass_dThe specific process is as follows: by analyzing the cutting force model of Mechant, i.e., the component force acting on the shear plane in FIG. 2, an equation can be obtained from the force balance on the shear plane

Wherein sigma_dIs the dynamic yield stress, h_c,/sin phi, the length of the shear plane, K_bIs the fracture toughness of the material, w_cIs the cutting width which is equal to the back rake a of the cutting edge in the cylindrical turning test_p，F_cIs the main cutting force, F_tIs the feed resistance (B.Wang et al. int.J.Mach.tool. Manu.73(2013) 1-8). Further, the above formula is converted into the following form:

i.e. the interrelationship between cutting force, shear angle and dynamic mechanical properties of the workpiece. For different cutting layer thicknesses h_cObtaining corresponding cuts by cutting testsChip thickness h_chMain cutting force F_cAnd feed resistance F_tCorresponding main cutting force F_cAnd feed resistance F_tAre listed in table 2. Thereby, further calculating F_c/w_c-(F_t/w_c) tan phi and (h)_c/2) (tan. phi. + 1/tan. phi.). Finally, F is plotted and linearly fitted_c/w_c-(F_t/w_c) tan phi and (h)_c/2) (tan phi +1/tan phi), and obtaining the slope of the straight line, namely the cutting dynamic yield stress sigma corresponding to each alloy_d。

(5) Identifying the high-strength high-plasticity free-cutting alloy: taking the zinc equivalent of the silicon brass alloy as an abscissa and the quasi-static tensile yield stress sigma_sAnd elongation, and calculated cutting dynamic yield stress sigma_dAnd drawing a trend graph of each performance index along with the zinc equivalent as an ordinate, as shown in fig. 3. As can be seen from the figure, the quasi-static tensile yield stress σ increases with the zinc equivalent_sThe elongation is correspondingly increased, the cutting dynamic yield stress sigma is correspondingly reduced_dDecreasing first and then increasing. At dynamic yield stress σ_dOf a value less than the quasi-static yield stress sigma_sAnd the method is favorable for unstable thermoplasticity and saw-shaped chip generation, thereby having free cutting. Silicon brass alloys can thus be further classified into three types: quasi-static tensile yield stress sigma_sLess than 100MPa, elongation higher than 40% and dynamic yield stress sigma_dGreater than quasi-static tensile yield stress sigma_sThe low-strength high-plasticity difficult-to-cut alloy; quasi-static tensile yield stress sigma_sBetween 100MPa and 250MPa, an elongation between 40% and 15% and a dynamic yield stress sigma_dLess than quasi-static tensile yield stress sigma_sThe high-strength high-plasticity free-cutting alloy; quasi-static tensile yield stress sigma_sMore than 250MPa, elongation less than 15% and dynamic yield stress sigma_dGreater than quasi-static tensile yield stress sigma_sThe high-strength low-plasticity difficult-to-cut alloy. The silicon brass alloy corresponding to the high-strength high-plasticity free-cutting area has the comprehensive properties of high strength, high plasticity, easy cutting and the like, and the zinc equivalent corresponding to the area is excellent healdAlloy composition region of alloy properties. The use of the alloy in other areas is greatly limited, so that the effective identification of the high-strength high-plasticity free-cutting alloy is of great significance.

Compared with the prior art, the chip breaking capability of the silicon brass alloy material is quantitatively evaluated by correlating the geometric form parameters and the cutting dynamic mechanical property of the metal alloy chips, the method has the characteristics of simplicity in implementation, low cost and the like, and the defect that a stress-strain model needs to be established in the traditional test method considering the dynamic extreme conditions of the material cutting engineering is overcome. Meanwhile, the invention establishes a high-strength high-plasticity free-cutting quantitative identification method, which is beneficial to the component design of the high-performance silicon brass alloy and provides a powerful reference for the design of the novel silicon brass alloy. In addition, the dynamic yield stress σ in cutting of the present invention_dDown to less than the quasi-static yield stress sigma of the material_sThe method is beneficial to the appearance of unstable thermoplasticity and serrated cutting chips, so that the free-cutting silicon brass alloy is obtained, and the test method can also be applied to the test of the free-cutting performance and comprehensive performance of other metal alloy materials.

The above embodiments do not limit the scope of the present invention, and any person skilled in the art can equally substitute or change the technical solution of the present invention and its patent idea within the scope of the present invention.

Claims

1. The quantitative identification method of the free-cutting environment-friendly lead-free silicon brass with high strength and high plasticity is characterized by comprising the following steps of:

2) dynamic yield stress sigma_dAnd (3) calculating: the cutting test was carried out on a silicon brass alloy having a zinc equivalent of between 38% and 49%, the chips were collected and passed through a Mechant-based cutA cutting force model for calculating the cutting dynamic yield stress sigma when cutting silicon brass alloy with different zinc equivalent_d；

3) Quantitative identification of silicon brass alloy: taking the zinc equivalent of the silicon brass alloy as an abscissa and the quasi-static tensile yield stress sigma_sElongation and cutting dynamic yield stress sigma_dFor the ordinate, the quasi-static tensile yield stress σ is plotted_sElongation and cutting dynamic yield stress sigma_dA trend graph along with the change of zinc equivalent; silicon brass alloys are classified into three types according to the trend graph:

quasi-static tensile yield stress sigma_sBetween 100MPa and 250MPa, elongation between 40% and 15% and dynamic yield stress sigma_dLess than quasi-static tensile yield stress sigma_sThe high-strength high-plasticity free-cutting alloy.

2. The quantitative identification method of the free-cutting environment-friendly lead-free silicon brass with high strength and high plasticity according to claim 1, wherein the method comprises the following steps: the preparation method of the silicon brass alloy with different zinc equivalent in the step 1) comprises the following steps: mixing Cu, Zn, Si and Al according to the following mass percent, wherein the Cu accounts for 56-66 wt.%, the Zn accounts for 33-42 wt.%, the Si accounts for 0.4-1.5 wt.%, the Al accounts for 0.2-1.5 wt.%, and the B accounts for 0.003-0.01 wt.% and the Ti accounts for 0.03-0.06 wt.%; and the zinc equivalent X% of all the components of the brass alloy is between 39 and 49%, and the microstructure is an alpha + beta phase.

3. The quantitative identification method of the free-cutting environment-friendly lead-free silicon brass with high strength and high plasticity according to claim 2, characterized in that: designed by zinc equivalent rulePhase composition, zinc equivalent passing formula

4. The quantitative identification method of the free-cutting environment-friendly lead-free silicon brass with high strength and high plasticity according to claim 1, wherein the method comprises the following steps: the cutting test in the step 2) is carried out on a CNC lathe, the lathe is provided with a cutting force dynamometer, a cutting sample is a cylindrical rod, the material of a cutting tool is a commercial WC-8Co tool, the changed process parameter is a feeding speed f value, and the value of the feeding speed f is 0.05-0.3mm/r according to the common cutting parameter of the brass alloy.

5. The quantitative identification method of the free-cutting environment-friendly lead-free silicon brass with high strength and high plasticity according to claim 1, wherein the method comprises the following steps: in the step 2), the cutting dynamic yield stress sigma when the silicon brass alloy with different zinc equivalent is cut is calculated by applying a test scheme developed by J.G.William_dIs formed by a force balance equation

Calculating F_c/w_c-(F_t/w_c) tan phi and (h)_c/2) (tan. phi. + 1/tan. phi.) (values of(ii) a By plotting and linear fitting F_c/w_c-(F_t/w_c) tan phi and (h)_c/2) (tan phi +1/tan phi), the slope being the dynamic yield stress σ in cutting_d；

Shear angle phi of silicon brass sample

Determination of h_chIs the average chip thickness.

6. The quantitative identification method of the free-cutting environment-friendly lead-free silicon brass with high strength and high plasticity according to claim 5, wherein the method comprises the following steps: chip thickness h of serrated chips_chThe equivalent value of (A) is obtained by a simplified method

Is obtained, where H is the maximum height of the serrated chips, H_sIs the height of the serrations.

7. The quantitative identification method of the free-cutting environment-friendly lead-free silicon brass with high strength and high plasticity according to claim 5, wherein the method comprises the following steps: thickness h of the cutting layer_cEqual to the feed f value in the cylinder turning test.

8. The quantitative identification method of the free-cutting environment-friendly lead-free silicon brass with high strength and high plasticity according to claim 5, wherein the method comprises the following steps: the cutting width w_cEqual to the back rake amount a of the cutting edge in the cylindrical turning test_p。

9. The quantitative identification method of the free-cutting environment-friendly lead-free silicon brass with high strength and high plasticity according to claim 1, wherein the method comprises the following steps: in the step 3), the high-strength high-plasticity free-cutting alloy is applied to manufacturing of bathroom accessories, household hardware, radiators, electronic instruments and low-temperature pipelines.