This article presents a preparation method for a horizontally cast easily machinable brass rod. The composition, expressed in weight percent, consists of Cu (61.0 - 63.0 wt%), B4C (0.1 - 0.6 wt%), Bi (0.7 - 1.5 wt%), Pb (≤ 0.08 wt%), unavoidable impurities (total) (≤ 0.3 wt%), and the remainder (Zn). The process involves steps such as raw material proportioning, melting in an inert gas environment, horizontal casting, graphitization annealing, finishing, and product inspection. The core mechanism involves suppressing melt oxidation and reducing gas inclusions in an inert gas environment. Combined with the graphitization annealing process, B4C releases fine carbon particles, and the Bi element cooperates to enhance cutting performance and tensile strength. The tensile strength of the easily machinable brass rod is not less than 500 MPa, the elongation rate is above 4.5%, the alloy hardness is not less than 150 HV, the electrical conductivity is not less than 20% IACS, the cutting performance is equivalent to that of lead brass, and the cutting particles are length-stabilized and controlled within 5 mm. It can meet the application requirements of high-end equipment, electronic and electrical, mechanical and hardware, etc., and has good environmental friendliness and practicability.
The easy-to-machine brass rods, due to their excellent cutting performance, tensile strength, hardness and corrosion resistance, are widely used in various fields such as high-end equipment, electronics, machinery, bathroom, hardware, etc. Traditional brass rods often contain lead (Pb) to improve the cutting performance, with a lead content of no less than 2%. However, lead is toxic. With the increasing global environmental protection requirements, reducing the lead content and improving the cutting performance and mechanical properties of the easy-to-machine brass rods through the addition of other environmentally friendly alloy elements has become an inevitable trend in the industry development.
Currently, the preparation of easy-to-machine brass mostly adopts traditional semi-continuous casting or casting processes, which have problems such as uneven alloy composition, many internal defects (such as pores, inclusions), large anisotropy of cutting performance and mechanical properties; at the same time, the existing easy-to-machine brass mostly improves the cutting performance by adding a single element, which is difficult to balance the cutting performance and mechanical properties, thus unable to meet the usage requirements of high-end equipment, electronic and electrical, and precision machinery fields, limiting its application scope; and some products may have phenomena such as tool entanglement and tool damage during cutting, with unstable cutting particle size, affecting processing efficiency and product quality.
Horizontal continuous casting under inert gas protection has the advantages of anti-oxidation, continuity, adjustable cooling and traction rate, which can effectively improve the quality of brass rods; while boron carbide (B4C) as a new type of adding phase, after specific carbonization annealing treatment, can release carbon particles, which are dispersed and distributed in the copper matrix, and combined with Bi element, can not only significantly improve the cutting performance, but also make up for the deficiency of single element addition, balancing the mechanical properties, electrical conductivity and cutting performance of the material. Therefore, developing a preparation method for easy-to-machine brass rods based on inert gas protection, combined with B4C and Bi composite addition, and meeting specific performance indicators, has important practical significance and application value.