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This FAQ section has been compiled from a recent Q&A session during a webinar covering automotive applications for aluminum extrusions, however many of the questions are of a general nature that may be of interest to a wider range of readers. Click on a question to read the answer linked below.

Topics covered include:

ALLOYS

DESIGN

FINISHING/FABRICATION

GENERAL

JOINING

PROCESS


ALLOYS

Along the fatigue question, are there any alloys with infinite fatigue life...like steels?
"Infinite" is a high hurdle. Any material, steel or aluminum, can be bent to the point where the part will fracture.

What is the best material for a light weight and low cost design where strength isn't as critical?
6063 would be a good starting point

6063-T5 is known as great for thermal dissipation in extrusion of heat sinks, but what element within the alloy must we look for to maximize the thermal conduction?
Depending on the profile and other structural requirements, other alloys are even better heat sinks (1000 series and 3000 series), although they may not offer the threaded retention or other requirements.

How about the fatigue resistance of 6005A alloy?
6005A was created in part to address fatigue resistance of 6005. The re-alloying gives very good fatigue resistance

Can 6005A be H-treated to a T6 temp?
The latest Aluminum Standards and Data do designate T6 for 6005A. Previous versions did not.

Do any extrusion alloys contain lead?
Other than alloys within those families designed for machinability, lead is present in trace amounts only.

Can 6065 have a T3 temper and is it Lead free?
I believe this to be a primarily rolled product.

Is 6061 available in T3 and is it Lead free?
6061 is not available in T3. It typically requires water quench and is listed as available in T4, T5, and T6, as well as F, as extruded.

Is there more of a difference in TYPICAL 6061 vs 6005 mechanical properties vs MINIMUM guaranteed properties that you seem to be referencing?
Typical performance for elongation and ultimate yield is similar. The actual aging procedures utilized will dictate the actual mechanical properties vs. the standard.

What is the maximum OD tube and minimum wall thickness that can be extruded in alloys like 6061 or 6005?
Diameter is a function of press size. The chart in the presentation shows the availability of different diameters. Generally, the larger the diameter, the larger the minimum wall thickness - please go to "Find an Extruder" and locate possible extrusion suppliers for your needs. Work with them to understand their particular limitations. Smaller diameters can have fairly thin wall thicknesses (.040" for 2" tubular shapes, .045" for 3" tubular shapes, etc. again - specific extruders may be able to achieve better than this, or not quite this, depending on their equipment and process capabilities)

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DESIGN

In higher torque applications such as diesel powered vehicles, is aluminum cost effective given the need for higher frame strength?
Yes - given you account for the moments of inertia for the frame. The ability to vary wall thickness helps make extrusion cost effective.

Do you have any experience in using aluminum extrusions for engine components (con. rods, crank shafts, turbos, EGR coolers, fuel and oil filters, coolers....etc)?
Yes, but not recip. components. For example, a unique "spiral" extrusion is used as an impeller in superchargers found on a number of Audi and Corvette models in lieu of a cast part. Read more about the Supercharger Impeller here.

If an extrusion is to be bent...what special design features may need to be included in the extrusion design to allow for a 'cleaner' bend?
Design features can play a significant role; however, bending process methods are extremely important to the end result.

Are there any examples of Al B-pillars made by extrusions?
Yes. Several are in production and more to come.

Is there any reason why Aluminum Extrusion use would be different in automotive than for aircraft?
In both, objectives are similar - low weight with critical strength requirements. The alloys used may differ, with 6000 series more typical in autos and 7000 more likely for aircraft - due to differing ultimate performance requirements. Note also that 7000 is often more costly to produce due to low extrudability

Fatigue life can be another factor in design. Aluminum typically does not have an infinite life in cyclic loading applications. What alloys or tempers provide better performance when considering fatigue?
There is a broad range of alloys tailored to meet specific design criteria for better performance when considering fatigue.

What can be done to reduce fatigue life in aluminum extrusions when compared to steel in auto applications?
Specific alloy and processes can be developed to improve fatigue life.

Which material provides the best energy absorption and repeatable performance through axial collapse of an extruded front crush tip during a high speed impact event?
Based on design criteria, several alloys and processes offer excellent energy absorption.

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FINISHING/FABRICATION

Is there any special prep or paint required for painting aluminum?
Typically a surface treatment is used prior to paint - liquid or powder- to seal the surface and promote adhesion

Given today's OEMs constant chase of achieving 13.5 PH resistance with anodized aluminum, is there a series that would work better for trying to achieve this goal? Why?
5000 and 6000 alloys would be best because they anodize the best. Chemical resistance involves special sealing techniques as well as adequate anodic coating thickness. A 13.5 pH means you have a strong alkaline. Experience shows that the suppliers sealing additives only work on mild alkaline (not strong). For example, the cleaning liquids in an automatic car wash uses a pH around 9 to protect the car trim, because an anodic coating is normally resistant up to pH 8. There are sealing systems on basic Silicate chemicals which give a resistance >pH 13. But then the anodic coating is so alkaline resistant that it is hard to remove the anodic layer in hot alkaline solutions. The disadvantage is that the silicate sealed layers have minor acid resistance. You can read more about this silicate sealing systems in the book "The Surface Treatment & Finishing of Aluminum & Its Alloys" by P.G. Sheasby & R. Pinner. Refer to the chapter on sealing methods. (Answer provided by The Aluminum Anodizers Council's Technical Panel; www.anodizing.org)

Anodizing reduces fatigue properties. Paint typically reduces the coefficient of friction. What coatings are available that do not reduce friction or fatigue characteristics?
You can read more about silicate sealing systems in the book "The Surface Treatment & Finishing of Aluminum & Its Alloys" by P.G. Sheasby & R. Pinner. Refer to the chapter on sealing methods. (Answer provided by The Aluminum Anodizers Council's Technical Panel; www.anodizing.org)

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GENERAL

How does the price of aluminum extrusions differ for vehicles (compared) to standard extrusion?
In general, custom extrusions will be more costly than profiles from an extruders "standards" catalog, due to tooling costs, production quantities, etc. However, extrusion tooling is relatively inexpensive, so the difference is often not that great; and when the ability to design-in specific desired features is considered, a custom part may be less than a machined standard.

What are some inspection methods and quality standards in extruded aluminum designs?
Inspection is similar to that with other metal forming. CMM, video measuring, hand tools. Also a variety of metallurgical tests are employed - tensile, fracture/toughness, etc. Standards are defined by the Aluminum Standards and Data manual published by the Aluminum Association, though often extruders perform to higher levels.

Is the longitudinal welding for hollow profile a limitation for the application in auto parts?
Often the longitudinal (die) weld is NOT a limitation at all - extruded hollow parts are used successfully in severe structural applications regularly. Depending on the application, special attention may be required to ensure that the billet-to-billet weld (which also extends along the initial length of the extrusion) is minimized or removed. This can be done through die design and through proper process planning

Can extrusions be clad? What difficulties are introduced with clad extrusions?
Yes. Dependent on the requirements and specification

Is there a location for inventoried shapes that are searchable based on size, shape, material?
Many extruders have a "standards" shape list, but frankly, for many applications the low cost of tooling an extrusion die suggests that a part customized to the exact use, putting material exactly where needed, is a better choice. The exception to this may be for "one-off" applications.

How is the supply base both in NA and overseas; are there global suppliers available?
There are over 125 extruders in North America, operating about 500 presses in nearly 200 locations. Of course, not all of them are active in the automotive market, though an increasing number are. You will find similar robust supply networks in Europe and Asia, with smaller - but still highly competent - supply bases in South America and MENA. A small number of extruders are global in scope.

When using an extruded aluminum profile to channel thermal oil, what are the upper temperature ranges? i.e. 240 C 300 C or higher? The profile would have a wall thickness of 1/2"?
At temps approaching 300 C the tensile strength may drop as much as 90%.

We have known these qualities of Aluminum alloys for quite some time. Why has the auto industries not thought about using Aluminum sooner? What are the problems/concerns?
Engineers and designers are simply NOT often exposed to aluminum extrusion in their formal educations. I graduated as an engineer from Penn State in 1980, and since my family business was the largest manufacturer of ladders in the world (Werner Co.), I desperately wanted to obtain an education in aluminum metallurgy, extrusion and fabrication. I had to rely on my uncles to provide me with technical information that I could use to craft self-study courses with my technical professors, as there simply were NO courses offered! In addition, on a per-pound basis, aluminum is more expensive than steel; thus unless weight reduction has value (as in significantly improving fuel economy) aluminum has been limited to niche applications due to its economics.

In one of the slides, light weighting from Al extrusions was shown to contribute only 15% towards meeting the 54.4 mpg, while transmission (I think) contributed 50%. Are there any applications of Al extrusions for the 50% share of the pie?
The 15% estimate was developed by Ducker Worldwide based on OEM's platform development programs. The 50% share of mileage improvement is expected to come from improvements to engines, transmissions (and we are already seeing 8-speed automatics), aerodynamics, friction reduction, etc. Extrusions may have a role in some of these areas - as components of supercharger or turbocharger systems for example, but those applications are typically not weight driven. The 15% contribution is primarily weight driven. FYI, the remaining 35% improvement is projected to be related to alternative power trains - hybrids, electrics, etc.

As a heat exchanger component, how many extruders can provide "twisting" of the tubes when coming off the die?
This is proprietary to individual extruders.

Do Extruder suppliers also assemble (Weld) assemblies like the Mercedes Floor used in case study?
Many can. The "Find an Extruder" function on aec.org provides information about specific extruder capabilities, including fabrication

Does aluminum have a higher market price in Europe or North America and why?
I cannot comment on the pricing for sheet or cast products, but European extrusion pricing has typically has been somewhat higher. Historically this has reflected market structure and energy and labor costs. Recently this gap has decreased.

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JOINING

What are some advancements/best practices in joining aluminum extrusions to dissimilar metals?
Aluminum alloys can have a galvanic reaction with some dissimilar metals. The corrosion occurs because of direct connection between the metals with an electrolyte (water, etc.) From a high level viewpoint, small amounts of aluminum will sacrificially corrode in this situation (a small aluminum fastener in a large mass of steel, for example). Small steel parts do not have this same problem. Often, other materials can be substituted (some stainless steels do not have the same level of galvanic reaction as plain steel, galvanized steel, where the galvanized coating is intact, offers protection, etc..) The aluminum alloy and other material can also be separated by a bituminous material, or, very commonly used, by adhesives.

For a durable structural bond what is the preferred pretreatment (urethane adhesives)?
Individual adhesive manufacturers will suggest a pre-treat. Usually it calls for an acid or caustic pre-treat to remove the natural aluminum oxide surface, similar to preparing for paint.

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PROCESS

I don't understand the "welding back together" of hollow extruded parts. Is it caused by the heat generated as the billet is forced through the die essentially melting them back together, or is there some other catastrophic mechanism that compels the grains to re-bond?
It is often thought that aluminum melts as it passes through the die. This is not the case. Rather, the high pressures involved cause a "solid state" weld, similar in concept to friction stir welding.

Many impressive complex sections were shown. Are any oxides, inclusions, or other discontinuities present at the "weld" zone where billet flows through the die come back together?
Two answers: For direct extrusion (MOST COMMON), the skin of the billet encounters friction as it is pushed through the container. The oxides and contaminants are contained in the skin. The flow of the material is such that the skin collects at the back of the billet, at the face of the dummy block. The extrusion process is stopped before this "butt" extends into the extrudate, and the butt is scrapped. For indirect extrusion (fairly uncommon), the billet is often "scalped" and/or scrubbed clean before extruding; in indirect extrusion, the surface of the material does extrude into the extrudate.

What is the nature and extent of the so-called "stretching" mentioned following extrusion? I assume this is different than straightening after heat treatment.
Extrusions emerge from the press at high temperatures (often 932 d.F. or higher), and are cooled by still or forced air, water mist, water spray or immersion in an water tank depending on the profile geometry and the alloy. Subsequent cooling on the "cooling table" can lead to gradual "bows" along the extruded length. Stretching is done to virtually ALL extrusions, where the profiles are gripped at each end and stretched in a controlled fashion (usually in the 2-4% range). This has VERY little effect on cross sectional dimensions (although channels can see their gaps altered) - in any case, the extrusions are designed so that the tolerances meet the customer requirements AFTER stretching, since this is part of virtually every extrusion process.

What problems occur with a less extrudable material? Tolerance, shape flexibility etc..?
As extrudability goes down, issues with tolerances, straightness, etc. go up. These can be addressed given the shape, application and needed quench.

Does aluminum age harden, specifically a material such as 3003/H14P?
Extruded 3003 (p is a sheet spec) does not age harden.

Can you comment on design limitations when considering bending extrusions into curved shapes?
Here you'll want to consult with your extruder. A lot depends on the specific shape and alloy. Try to design the profile so it doesn't have to be bent the "hard way". Also the bend tooling will need to be designed to keep key features from moving

What is the typical surface finish range easily achievable when extruding?
Excellent surface finishes are possible with proper tooling consideration.

On a 10 inch OD and a 9 inch ID 6005 T6 extruded tube, what would the typically best achieved tolerance be on the OD and ID?
Beyond standard tolerance table, see individual extruders for specific capability.

Does a TIG welded aluminum car frame needs to be heat treated after welding?
Not necessarily. Either pre or post heat treat will work. The decision may be driven more by requirements for bending

What are typical Tongue ratios, extruded? And is there a big difference in the TR on narrow channel vs a wider channel, say .250" narrower or wider?
Most extruders can easily extrude semi hollows with a tongue ratio of 3 or below - greater tongue ratios can also be extruded but may require higher billet temperatures and subsequently slower extrusion velocities, using more hours/ton of extrusions and increasing costs or with more die breakage (also increasing the expected cost). Tongue ratio is defined as the area of the void divided by the "base" of the steel tongue that would restrict the flow of material^2. For example, for a simple narrow C-channel with a 1/2" gap 3" high, the tongue ratio at the worst point (the full tongue in this case (refer back to the presentation to see a simple way to make the tongue less severe) would be (0.5*3) in^2/ (.5^2) = 6.0

Can aluminum extrusions be run through a PVC (or other material) extrusion process for a surface layer of the second material?
Yes, co-extrusion of previously extruded aluminum profiles with polymers or other materials are commonly used in automotive applications.

What prevents carmakers from using more aluminum extrusions? What role does hydroforming play?
Past practice has been to use steel, in part because steel is widely taught (in materials and engineering classes), in part because steel is cheaper on a per-pound basis. The current pressure to reduce weight to hit CAFE standards is motivating designers to reduce grams, hence more aluminum.

Hydroforming is used on particularly challenging bends, complex bends, tight radii, where features need to be controlled tightly and the higher cost of hydroforming (vs. stretch bending or other processes) is merited.

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