6xxx Series Alloys

6000-series alloys are most frequently used for extrusion, as they provide a good balance of strength, corrosion resistance, weldability, machinability, and surface finish,. For these reasons, the 6xxx alloys are  used in a wide variety of applications, including transportation, architectural, consumer products and electrical. Silicon (Si) and magnesium (Mg) are the major alloying elements in this series.

Effects of alloying elements

The addition of alloying elements modifies the properties and characteristics of aluminum. Pure aluminum is very soft; alloying elements are needed to provide higher strengths needed for structural and high-pressure applications, and to enhance other attributes.  Aluminum alloys are grouped by major alloying elements. 

The number of alloy variants in the 6xxx series is broad. As of 2022, in total there are 564 aluminum alloys registered with The Aluminum Association and of those 110 are in the 6xxx series;  that excludes proprietary variants that may have been developed for specific applications

6xxx Alloy Strength

As this chart illustrates, there is a range of Si and Mg for each alloy, thus there can be significant variations in behavior and performance for a given alloy depending on the actual mix employed. Note the overlaps between alloys of different groups. Any one alloy can have a variety of formulae and, therefore, can be “tweaked” to optimize properties. 

Certain alloy variants are better for certain applications. For example, in automotive applications, AA6082 is often used for automotive applications such as bumper beams, chassis, intrusion beams and structural parts due to its high strength. AA6063 is commonly used for building products, auto trim parts, heat sinks and electronics housings because high strength is not needed for these applications.  Note however that component geometry can often allow “lower strength” alloys to perform in “higher strength” applications.

Extrudability Index

While aluminum alloys can be strengthened by increasing Mg and Si, it’s important to understand that higher strength alloys can directly impact manufacturability, tolerances, recyclability, and cost.  Extrudability – how easily or quickly an alloy can be extruded – is shown in the chart above for some common aluminum alloys. As the extrudability index decreases, costs go up since additional press time is required and yields often decrease. The good news is that there are alternatives to simply specifying a higher strength alloy to provide stronger components – and that is geometry. Specifying a highly manufacturable alloy and with the proper part geometry (e.g. a multi-void hollow) can yield excellent results.. In addition to the manufacturability, improvements in tolerance, cost and repeatability are possible through engineered geometries.

To fully consider alloy, geometry and process trade-offs, talk with a qualified extruder early in the design process. They have experience with helping customers tweak designs and alloys to reduce cost while obtaining the best properties for the needed application.