DN Staff

August 25, 2010

5 Min Read
Understanding Aluminum Alloys

One of the most important things to understand about usingaluminum for part or product design purposes is that pure aluminum is only usedin a limited way commercially. The majority of extrusions are made fromaluminum alloyed with other elements. The most common elements used aremagnesium (Mg), silicon (Si), manganese (Mn), zinc (Zn) and copper (Cu). Mostaluminum extrusions are made from the following alloy series: 1000 series Al; 3000series Al + Mn; 5000 series Al + Mg; 6000 series Al + Mg + Si; and 7000 seriesAl + Zn + Mg.

The 1000 series is non-heat-treatable and are often selectedfor products where high thermal and electrical conductivity are desired. Theyhave low strength. The 3000 and 5000 series also are non-heat-treatable and areoften used in drawn tubing for highly ductile applications and printercomponents. The 5000 series is mostly used in extremely corrosive environmentssuch as marine. The 6000 and 7000 series are heat-treatable. They are the mostcommonly used extrusion alloys and have a wide range of applications.

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6000 Series

For most extrusion applications, the 6000 series aluminumalloy is often the optimal choice. The 6000 series alloys are termed "softalloys" because they are easy to weld and offer good resistance to corrosion,even in marine environments.

The 6000 series has good extrusion abilities and can besolution heat-treated during hot working at the extrusion temperature. Solutionheat treatment enables some of the alloying elements, such as magnesium andsilicon, to go into solid solution and can be maintained in a supersaturatedstate on quenching. This homogenous material is subsequently age hardened toobtain the required mechanical properties.

Among the 6000 series, the 6060 alloy offers low-to-mediumstrength and is easy to extrude even for complicated cross-sections. Thismaterial is well-suited for anodizing, both for decorative and protectivepurposes. It has good formability during bending in the T4 condition (i.e., thealuminum has been solution-quenched and naturally aged at 70F for 5-10 daysbefore delivery to the customer). This material is highly suitable foranodizing, both for decorative and protective reasons.

The 6063 alloy has slightly higher strength than 6060, butis also marginally more difficult to extrude, especially if the cross-sectionis complicated.

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Heatsink Application

Aluminum is considered an excellent choice for heatsinksbecause it absorbs heat better than other metals. In a recent case, Hydro Aluminum's metallurgical and extrusiondesign teams worked with a lighting fixture manufacturing company to extrudecomponents for a heat sink, framework and connecting rails for a new modelfixture.

The Hydro technicians teamed with the company's die vendorsto develop a die to make the heatsink shape which required a difficult toextrude tongue ratio combined with a thin wall design. For the first test run,Hydro chose a standard 6063 aluminum alloy. Both the 6060 and 6063 alloysprovide excellent extrusion ability and surface finish for lighting, windowsand doors, marine, ventilation and consumer products.

During the first run with the 6063 billet, the tongues brokeout of the die at high breakthrough pressures. To address these issues, Hydrodrew on its experience in developing a new alloy recently that falls into the6060 category. This new alloy improves manufacturability while delivering thesame performance as other 6060 and 6063 alloys. It is well-suited for complexextrusions, allows for better surface finishes, and is a useful alternative tosome 6063 solutions.

Hydro recommended switching to its 6060 alloy with the ideaof tweaking it so that it could be extruded at lower breakthrough pressures, asthis would give better overall extrudability and respond better to anodizing,which also happened to be the customer's finish option for this component.

With the go-ahead from the customer, Hydro ran a short runorder of the tweaked 6060 alloy through its casthouse. While the 6060 alloy wasbeing prepared, plant operations made a second die with a design modificationto make it easier to extrude the heatsink tongues.

The first run through the press resulted in some of the finsbeing out of shape due to tongue defection and flow variance. Recognizing thatthis issue could be addressed before going into full production, the customeragreed to move forward with prototypes. Hydro was able to run the new 6060alloy through the press with a lower breakthrough and faster speed.

Hydro operations employees then met with the customer to adjustthe die design to eliminate the tongue deflection. The result was a new roundof samples that proved successful.

Aluminum's Green Side

The choice of material is a critical decision in all productdevelopment designs. Sustainability issues related to material choices arebecoming an increasingly important of the design process due to regulations insome industries as well as corporate initiatives to be more environmentallyconscious.

Aluminum is an excellent choice when considering itsenvironmental impact compared to other metals. All extrusion-based componentsproduced by Hydro Aluminum in North Americause primary-grade billet, which contains more than 70 percent recycled content(produced using Hydro's proprietary remelt technology). As a result, only 5percent of the energy used in primary aluminum production is needed to remeltaluminum.

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