Which alloy characteristic usually leads to high machinability ratings?

The presence of additives in an alloy typically leads to high machinability ratings. Additives such as sulfur, lead, and phosphorus can modify the microstructure and enhance the machining characteristics of the metal. For instance, sulfur can improve chip breaking, while lead can provide lubrication during machining, resulting in a smoother and more efficient cutting process. These improvements allow for better tool life, reduced cutting forces, and higher-quality surface finishes.

In contrast, other characteristics like high brittleness can make the material more prone to cracking or breaking during machining, which negatively affects machinability. Low tensile strength may suggest a softer material, but it does not necessarily improve machinability as other factors like ductility and thermal properties come into play. High density, while a physical characteristic of a material, does not directly correlate with machinability because it depends more on the material’s ability to withstand machining forces without excessive wear or deformation.