What Are the Advantages of Aluminium for CNC Machined Parts

Aluminium is one of the most popular materials for CNC machined parts – here are six reasons why.

1. Quick to machine

If you ask any CNC machining manufacturer then they would point out how easy it is to machine.  Aluminium is very dimensionally stable so you can cut a lot of it away and still keep residual stress in check.  Using carbide tooling and modern coolants you will get a great finish and it can be bead blasted for a matt finish or anodized for a consistent aesthetic finish and additional corrosion resistance.

And best of all this machineability will help keep the cost of your part down.  But you select a material based on what characteristics you need from your part – so what else has aluminium got to offer?

2. Great strength to weight ratio

Aluminium is lighter than most metals, so if you are looking to save weight it’s a great option.  While pure aluminium has a tensile strength of less than 100Mpa, it can be hardened as follows:

• Alloying, mixing with other elements improves the grain structure.
• Heat treatment, heating and then cooling at a specific rate to create ideally sized crystals.
• Work hardening, deliberately deforming the metal to change its grain structure. This is normally done whilst heat treating (rolling for example) but it can be done afterwards (forging).

A “temper” designation shows the exact condition, or strength, of the resulting material, H for “hardened” and T for “thermal”.

It’s worth noting that most aluminium alloys have a higher strength to weight ratio, or specific strength, than stainless steel 316L. 

While Titanium is a clear winner from the table below, when stiffness and weight saving is important, the high strength aluminium alloys are a great cost effective alternative if budgets are an issue.

3. Wide choice of alloys and material properties

In fact, because aluminium is such a great base material to work with, there are a lot of alloys available, each of which have different properties and uses to meet your needs. 

These are grouped into nine different series with each series numbered by a thousand, so for example 6000 series. This is then further subdivided by a number.  Generally, the closer the number of the aluminium grade to another the more similar they are, so 5082 and 5083 are nearly identical.

Here are some of the more popular grades:

• 2024 – Aerospace grade, with high fatigue strength, it trades ultimate tensile strength (UTS) for more ductility/toughness, by alloying with copper.
• 5083 – Marine grade, with good corrosion resistance, as it has higher magnesium content.
• 6082 – General purpose and aerospace grade, it has a good blend of strength, ductility and corrosion resistance which make it versatile and commonly used. This is achieved by alloying with a mixture of magnesium and silicon (it is also closely equivalent to 6061).
• 7075 – High strength aerospace grade, good balance of properties, particularly where high static loads occur. It can be heat treated and contains more zinc, as well as magnesium and chromium.

4. High corrosion resistance

While corrosion resistance will vary between grades, aluminium is an excellent choice if you need this from your material.  The metal and its alloys have an ideal affinity for oxygen – metals that are too reactive like magnesium will oxidise easily, while less reactive metals form a loose oxide layer such as rust on iron and steel. 

In contrast when aluminium is exposed it forms a passivating layer of aluminium oxide that seals the surface preventing further oxidisation and erosion. This layer is “self-repairing” even if scratched, so the material may not need painting or surface treatments, giving you a cost saving on manufacturing and life-time service costs. Having said that you can enhance this natural corrosion resistance by anodising it – but more on that later.

5. High conductivity

While copper is often the go to material for conductivity, electrical components often use aluminium since it is much cheaper and lighter.  In fact, it is often used for busbars, battery cables and connectors, particularly in automotive and EV applications.

It’s good thermal conductivity also means that it commonly used for heat sinks and heat dissipation.

6. Recyclable

With sustainability high on most people’s agendas, it is great to hear that an estimated 75% of all aluminium produced is still in use. Recycling aluminium uses much less energy than producing it and as long as we can keep impurities in check, it can be used time and time again.

We’ve already touched upon how machining this material can give you a great finish and how aluminium is naturally corrosion resistant, but for added aesthetics you can even have it in a number of different colours by anodising it.

This is a surface finishing procedure that not only increases the wear and corrosion resistance of a material, but it makes it easy to add colour.  At Protolabs we offer both decorative anodising, or type II, as well as type III which adds an even thicker layer of 50 µm for extra protection.

The process increases the thickness of the passivating oxidised layer by using acids and an electrolytic process. Aluminium oxide is a hard ceramic, so this coating really is hard wearing.

Material selection for your part is crucial and will depend on what characteristics you need from it. Aluminium is often a great choice for the reasons outlined above, but there are many more metal and plastic options available. To help you make the right choice for CNC machining we have produced a pocket-sized CNC materials selector as a quick reference guide. 

When you upload a CAD model to our website, our quoting tool calculates what can be machined within our capabilities, and what has risk. Its conclusions are clearly spelled out in the quote, giving you a chance to adjust the part design if so desired and spin the quoting wheel again. If you're ever in doubt, however, contact our applications engineers at +44 (0) 1952 683047 or [email protected]