ABSTRACT: adding other elements into simple brass makes it become complex brass. At this time, the complex brass has high strength, high wear resistance and high impact resistance which the simple brass does not have. The strengthening way is solid solution strengthening and particle strengthening. When the alloy is designed, the expected value of the alloy design will be reduced if the processing technology and heat treatment system are not properly formulated. Key words: Complex Brass; Solid Solution Strengthening; particle strengthening; Alloy Design Drawing classification number: TF805.1 document identification number: A article number: 1006-0308(1999)05-0040-05

1. Foreword in recent years, more and more high requirements are put forward for engineering materials in some places where the use environment is very bad. Simple brass, simple aluminum brass and simple manganese brass can not meet the actual use requirements, forcing material designers to design more qualified new alloys according to different special needs. In particular, the urgent demand for wear-resistant, erosion-resistant, high-strength and complex brass in the industries of aviation, navigation and automobiles has caused countries to invest a great deal of manpower and material resources in this field, a batch of new grade alloys have been developed successively. The alloy design of complex brass includes the design of material composition, the design of processing technology and the design of heat treatment system. 2. In order to improve the strength of materials, the strengthening principle can be achieved by solid solution strengthening, particle strengthening and dislocation strengthening. The complex brass design process utilizes both particle strengthening and solution strengthening to provide high strength and wear resistance.

2.1 solid solution strengthening is the increase of flow stress caused by the interaction between solute atoms and moving dislocation in solid solution. When solute atoms are added to a solid solution, the size difference between Matrix and solute atoms is expressed by the parameter of "size mismatch" . When there is a size mismatch, the interaction energy with the dislocation is generated by the strain field caused by the distortion of the local crystal lattice. For spherical distortion, the maximum force of edge-type dislocation is F = b 2(1) , where F is a hyper-elastic force, the shear modulus BA The superelastic force is proportional to the size mismatch parameter. The atomic binding force of the crystal is changed around the solute atom, which can be expressed by the parameter of "modulus mismatch" . When there is a modulus mismatch, because the dislocation strain field is proportional to the Shear Modulus, therefore, the meso-elastic interaction energy in the crystal is: e = WS + XWd (2) , where: the meso-elastic Interaction Energy Between e-x dislocation and solute atom is directly proportional to the shear modulus mismatch parameter, the bulk modulus mismatch parameter, the bulk modulus mismatch parameter, the Ws-shear energy density, the dilatancy energy density, and the bulk modulus mismatch parameter. In this way, the change of F and e due to the existence of solid solution atoms leads to the increase of the deformation resistance of the crystal and the effect of solid solution strengthening.

2.2 The high strength of the two-phase alloy is produced by the interaction between the particle-strengthened dislocation and the metallurgical barrier. In general, precipitating particles are the most effective obstructions. The particles interacting with the dislocations can be divided into punctate and ductile obstacles. The point obstacles have direct physical contact with the dislocation, while the ductile obstacles only interact with the dislocation within a limited distance. In addition, particles can also be divided according to the way the dislocation swept, the dislocation can be cut off the particles known as a weak barrier, can not be cut called a strong barrier. This creates two mechanisms, the cut-through mechanism and the bypass mechanism. When there are particles, the flow stress of the metal is increased, and the dislocation movement of the metal is resisted by the particles. In formula (3) , the maximum local stress Max is inversely proportional to the radius of the particle, that is to say, the smaller the radius of the particle, the better the strengthening effect. The commonly used strengthened alloys have solute atoms with different strength and mechanism of interaction, resulting in complex strengthening. For example, solid solution strengthening plus particle strengthening, solid solution strengthening plus dislocation strengthening. For complex brass alloy design, solid solution strengthening plus particle strengthening is used.

2.3 wear resistance of complex brass in the environment with wear and erosion, the alloy design process should not only consider the high strength, but also consider its wear resistance, impact resistance and other requirements. In the use of complex brass, the friction mode is actually the wear caused by the metal blocks sliding past each other. The gradual change caused by the impact between two metal blocks is called "erosion wear" . It has been proved that some hard phase particles are distributed in the Matrix containing soft phase, which is an ideal wear-resistant material. In the wear process, some hard phase particles fall off from the Matrix and exist on the friction surface, so it is better to produce rolling friction. And because the Matrix has a certain toughness, it can make the material when the impact on the impact of the impact has been slowed down. According to the wear law, the wear volume is inversely proportional to the hardness of the material. W = KLH (4) : Wear Volume; friction coefficient; normal load; hardness of material.

3. In the alloy design, AL, MN, Ni, Fe, SI, Sn, Ti and other elements are added into the simple brass. The alloy with Al as the third main element is called complex aluminum brass, and the alloy with MN as the third main element is called complex manganese brass. At present, the two kinds of complex brass are widely used in engineering materials. The complex aluminum brass is taken as an example to illustrate the alloy design. The more complex aluminum brass used internationally is shown in Table 1. These alloy plates are used in different occasions, the various properties of which are also different. In order to meet the needs of automotive industry and aviation industry for wear-resistant complex aluminum brass, many new brands have been developed, such as Hal61-4-3-1, HAl63-3-1, HAl65-5-4-3, HAl67-5-3-1, H59GM, H59GM- 1, etc. .

3.1 Al is the effective element to strengthen the parent phase. The atomic radius of Al is 1.43, larger than that of Cu (1.28) and Zn (1.37) . When AL displaces the CU or Zn atoms in the crystal lattice, the natural stress field of the crystal changes locally and the crystal lattice is distorted to some extent, thus, the elastic stress field of the crystal is changed. When the alloy deforms by moving dislocation under the action of external force, the elastic stress field interacts with the moving dislocation, which increases the deformation resistance of the alloy and enhances the strength of the alloy macroscopically. The increase in flow stress is proportional to the concentration of solute atoms and is called progressive hardening. The addition of Al to Cu-Zn alloy can greatly improve the stability of the phase and increase the strength of the Matrix. The content of Al also has a great influence on the relative ratio of phase and phase. Because AL can reduce the phase zone, generally speaking, the hot workability of the alloy can be reduced if the AL content exceeds 8% . Generally, the control of AL content is suitable for the presence of little or no Al.

3.2 Fe, SI effect the solubility of Fe in brass is very small, over the solubility of Fe is precipitated by iron-rich phase particles as "artificial crystal nucleus" to refine the ingots grain. Moreover, the recrystallization temperature can be increased, the recrystallization grain growth can be inhibited and the strength of the alloy can be improved. Si can form intermetallic compounds with other elements in alloys. For example, FE3SI can be formed with Fe and MN5SI3 can be formed with MN. When the SI content is more than 2.0% , the alloy is brittle, and less than 1.0% , the intermetallic compound is too little. It should be noted that with the increase of Fe content, the morphology of Fe-rich phase particles changes from the granular state to the massive state. Phase structure of the final processed HAl61-4-3-1 alloy. The results show that the particles of iron-rich phase are small, uniformly dispersed and spherical in shape. The particle size is about 210-1m, which is consistent with the fact that the reinforced particles must be dispersed and have a size of sub-micron. On the one hand, these fine particles block the dislocation movement when the metal deforms, so that the dislocation line must climb over the particles to move forward, and enhance the flow stress of the material. On the other hand, it can be detached from the Matrix and stuck between the two friction surfaces in the process of wear, resulting in rolling friction, reducing the volume wear of the alloy, playing a wear-resistant role.

3.3 The solubility of MN in brass is higher than that in brass at room temperature, which is up to 4% , but the solubility of MN in brass is decreased due to the influence of other elements. Mn can also combine with Si to form hexagonal Mn5Si3 with lattice parameters a = 6.9 and C = 4.8. In the casting products, Mn5Si3 is rod-shaped and is broken into blocks during the processing. Because the hardness of Mn5Si3 is very high, the wear resistance of the alloy is improved. Ni mainly improves the corrosion resistance and toughness of materials. When NI is combined with Al, a spherical NI3AL can be formed, which leads to obvious precipitation hardening. However, Ni has the effect of inhibiting phase precipitation, which should be paid attention to. Sn can dissolve a little in phase and (+) brass, which can inhibit dezincification, improve the corrosion resistance and wear resistance of the material, but Sn can cause reverse segregation of the INGOT.

3.4 The relative content of phase sum not only ensures that the alloy has certain strength and hardness to make it wear-resistant, but also ensures that it can withstand certain impact and has certain toughness. This makes the alloy phase and the relative content of the phase have certain requirements. It has been pointed out that the properties B of the alloy are 550 MPA, 10 are 8.0% , HB are 146 kg/mm2 when the content of phase and phase is 66%/33% , and the content of phase and phase is 27%/62% when the content of phase and phase is constant except Cu, Zn and Al, b = 760 MPA, 10 = 7.0% , HB = 179 kg/mm2. It can be seen that the tensile strength and hardness of the alloy with high relative content of phase are high. In general, in order to reduce the cost of materials, to make the Zn content as high as possible, in order to avoid more phase and reduce the toughness of materials, Zn content in alloy design should have a control upper limit. AL decreases the phase region significantly. Therefore, when designing the phase structure of the alloy, the above factors should be considered together, and the processing technology and heat treatment system should be taken into account to obtain the ideal phase structure.

4. Processing Technology and heat treatment system when the alloy is cast into Ingot, the establishment of processing technology and heat treatment system becomes the key factor to decide whether the material is qualified or not. The processing technology includes heating temperature, processing rate and so on. The heat treatment system includes intermediate heat treatment and final heat treatment. Therefore, processing technology and heat treatment system should be based on the alloy composition, performance parameters requirements, changes in phase structure and other factors and combined with the phase diagram to formulate. If the processing technology and heat treatment system is not reasonable, even if the production of qualified INGOT, the final product may not be qualified. The processing technology and heat treatment system are reasonable, the particle is small and dispersed, there are a few phase in the grain boundary, and a few block phase are distributed in the phase. It has HRB & GT; 100 and high hardness. The processing technology and Heat Treatment System of Hal 61-4-3-1 alloy are not well established, and the heat preservation time of Ingot is too long before processing, which makes the development of strengthening particles larger, about 10 M. During the subsequent deformation, the resistance of the dislocation to climb over the particles increases, and the moving dislocation only drags the particles together for local motion. When the number of particles dragging along the dislocation line reaches a certain number, the deformation of the dislocation line increases and the tension of the dislocation line increases. When the tension of the dislocation line reaches a certain value, its energy is enough to get rid of the pinning of the particles, climb over the particles, and continue to slip forward. A chain-like particle distribution is left behind the dislocations, and this chain-like particle distribution is actually the common effect of many dislocations. In order to illustrate the importance of the heat treatment system to the microstructure of the alloy, a series of experiments are carried out to confirm this problem. Alloys of the same composition are treated in three different ways. (1) HAl67-5-3-1 alloy was heated to 900 °C for half an hour and air-cooled, when the Matrix was phase and the block or willow-leaf-like particles with lighter color were phase, the hardened particles were precipitated from the Matrix and distributed uniformly. Under this condition, all the performance indexes are good, HB can reach 193 kg/mm2. Special attention should be paid to the existence of strengthening particles in the phase, which shows that solid solution elements and strengthening particles also play a strengthening role. (2) Hal 67-5-3-1 alloy was heated to 900 °C, kept for half an hour and quenched in water. After water quenching, the added elements were basically dissolved in the Matrix, but there were small point-like lead phase in the grain boundary and big block-like phase. Because there is no time to make the transition, the phase is kept to room temperature at high temperature. This makes the alloy at this time although has a higher hardness, but the elongation rate is lower, poor toughness. (3) Hal 67-5-3-1 alloy is selected, heated to 900 °C, kept warm for half an hour, and cooled slowly to room temperature for 24 hours. When the alloy is cooled slowly for a long time, the transformation is carried out sufficiently, and the phase content exceeds that of the phase, and the individual volume of the phase is much larger, forming a nibbling form of the phase. At high temperature, the particles of solid solution elements aggregate and grow up one another, some of which are in the shape of hexagon, some of which are in the shape of polygonal rods and triangles. Because of the precipitation of solid solution elements from the Matrix, and small strengthening particles have developed into large particles, which makes the alloy lost the original intention of strengthening alloy design.

5. Conclusion the design of complex brass is based on the requirements of engineering materials. The factors such as the choice and content of solid solution strengthening elements, the choice and content of particle strengthening elements, the relative content of phase and phase, the processing technology and the best formulation of heat treatment system are closely related to the quality of the final product. The alloy is designed as a systems engineering, and each element and factor should be taken into account. 

Source; china.com.cn, by Guo Shumei

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