What Makes Aluminum Alloy More Machinable Than Others?

Aluminum alloys have excellent machinability characteristics due to their high thermal conductivity, low density, and low melting point. However, some aluminum alloys are more machinable than others, which can be attributed to several factors, including:

Alloy composition
The composition of aluminum alloys can significantly affect their machinability. Some aluminum alloys, such as the 6061 series, include small amounts of lead or bismuth, which act as lubricants, improving their machinability. Other alloy compositions such as 7075-T6 are less machinable due to their composition of copper, which can cause tool wear and tear during the machining process.

Alloy structure
Aluminum alloys have different crystal structures that affect their machinability. Some alloys, such as the 1100 series, have a face-centered cubic structure, making them more ductile and easier to machine. In contrast, other alloys such as the 7075 series have a hexagonal close-packed structure, which makes them less ductile, more brittle and challenging to machine.

Manufacturing method
The manufacturing method used for producing aluminum alloys can affect their machinability. Cold-worked alloys, such as the 2024 series, have high strain hardening, which can make them more challenging to machine. Similarly, heat-treated alloys, such as the 7075 series, have a harder structure that can make them difficult to work with, especially when using cutting tools.

Machining process
The choice of machining process can also affect the machinability of different aluminum alloys. For example, drilling and tapping aluminum alloys require high cutting speeds and low feed rates to get good results and avoid work hardening. When milling aluminum alloys, high-speed machining with appropriate cooling agents could reduce the cutting forces and deliver a better surface finish.