Copper alloys containing lead are being replaced with low-lead containing alternatives for plumbing applications due to the current restrictions on lead content in components used in potable water applications. One of the alternatives is the family of copper alloys containing bismuth as a replacement for lead. It has been reported that this family of alloys develop fine to severe cracks during machining. These cracks cause reduced strength and loss of pressure tightness. The exact mechanism of cracking is not clearly understood. The cracking of castings is an intermittent problem encountered by foundries. This nature of the defect illustrates that there is a window of opportunity available to produce defect free castings. The foundries would like to establish this processing window and the major variables influencing the window. This information will help them to control their manufacturing process effectively to reduce/ eliminate the cracking problem.

Earlier work carried out on the characteristics of these alloys revealed that bismuth may promote intergranular cracking when improperly heated and cooled in the temperature range of 450 - 600F (225 – 275C). The interaction of bismuth with copper and grain boundary elements such as tin and zinc have been cited as possible reasons. These alloys have been shown to lose strength, under both static and dynamic loading conditions, beyond 482F (250C). However, it has not been possible to measure or determine the exact reason for cracking during machining. While a comprehensive investigation of factors affecting machinability of this and other No-Pd replacement alloys is being considered, currently the Task 1 study (Identification of variables promoting cracks in low-lead alloys) has been funded. This task will focus on collecting baseline data for machinability studies. Foundries will prepare test castings and subject them to a range of machining operations. Information will be collected during these machining operations on variables including: tool material, tool geometry, mode f operation (dry or wet), feed, speed, depth of cut, tool condition (sharp/blunt) and casting section size. Along with the information on machining the foundry variables will also be collected during this study. These include: alloy composition, melt control (gas, deoxidation, other additives, melting), casting parameters (molding, mold constraints, core) and fettling operation (heat evolved, impact loading).

This experiment will be conducted to identify the worst case scenarios where castings promote cracking. Most commonly used bismuth containing alloy will be used for this work. This can be C89520 or C89836. The steering committee will be consulted before the selection of the alloy. The data will be analyzed to select the most critical variables for full blown machining experiments. Efforts will also be made to collect more information on the machinability issue by conducting an industrial survey and workshop on the issue

Status Update: Microstructural analysis was conducted on samples exhibiting cracking at CWRU. A draft report on the machining results has been prepared. Those wishing information on participating in this study should contact the Steering Committee Chairman Jeff Sorenson, Neptune Technology Group, at This e-mail address is being protected from spam bots, you need JavaScript enabled to view it .