The Weld

The Steel Eyelet

The Aluminum Rim

Rolling

Rims

References: [1]: How It's Made: Aluminium Bike Wheels. Youtube. Discovery: Science Channel, 4 Dec. 2011. Web. 30 Apr. 2015 5083." [2]: Lyman, Taylor, ed. Metals Handbook. Novelyty: American Society for Metals, OH. Print. Joining Aluminum Alloys, [3]: ., [2]: Yazdipour, A. R., A. Shafie, and Jamshidi Aval. "An

Investigation of the Microstructures and Properties of Metal Inert Gas and Friction Stir Welds in Aluminum Alloy

The most common processing methods for aluminum bike

rims was researched. From the research we concluded

that the mountain biking rim was bent from a long

straight tube of extruded aluminum. Then, the rim wheel

profile tube was formed as a hollow shape using a spider

and die. Additionally, the two ends of the rim are welded

together before being heat treated [1]. The resulting

microstructure is shown above. Fine equiaxed grains are

present along with silicon, iron, and manganese

intermetallics. These impurities within the aluminum

matrix are too expensive to remove.

EDS analysis revealed Ni and Cr within the steel. Ni

stabilizes the austenite and Cr has anti-corrosive

properties. The eyelet material was likely drawn and

then formed as indicated by ghost lines parallel to the

drawing direction. The deformed δ-ferrite stringers are

present within an equiaxed austenitic stainless steel

matrix.

20mm

28mm

A vertical weld line is

present in microstructure.

There are elongated grains

along the weld line from

deformation. These flow

lines hints to some form of

butt-welding, where

solidification occurs under

external pressure. The

aluminum rim was likely

fusion-welded, due to the

presence of a liquid weld

pool [3]. It cannot be

confirmed if it was MIG or

TIG welded due to the

localized deformation at

the weld line.

David Burak and Spencer Fruend

Conclusions 1. The bulk of the rim is composed of 6XXX series aluminum. It was solution strengthened through likely Mg2Si particles. 2. The aluminum rim was extruded and then heat treated, resulting in fine equiaxed grains.

3. The ends of the aluminum rim were welded together, likely under pressure through fusion welding.

4.. The eyelet is composed of stainless steel, and was likely drawn and then formed. Ghost lines are present in the austenitic matrix

Introduction A lightweight high performance DT Swiss EX 5.1D bike rim was investigated.

The bulk aluminum alloy, the weld region of the rim, and the stainless steel

eyelet which houses the spokes were of interest. The rim was sectioned

accordingly, mounted, ground, and polished with standard metallographic

techniques. The aluminum was etched in Weck’s reagent for 12-15 seconds and

the stainless steel eyelet was electrolytically etched in 60% nitric acid for 15

seconds.

The macro photo of the

weld line shows the two

ends of the rim coming

together. The liquefied

metal solidified under

pressure during butt

welding. The solidified

region from the fusion zone

can be seen at the bottom of

the image. The excess

material on the outside of

the rim was machined off.

Weld Line Aluminum Rim

Weld Line

EDS and SEM was performed on the sample and

demonstrated alloying elements of Mg and Si, most

commonly in the form of Mg2Si micron sized particles . .

Magnesium and silicon are the major alloy additions in

6XXX series aluminum. These Mg2Si particles solution

strengthen the aluminum in the heat treated condition by

blocking dislocation motion. The Si enhances the strength

and Mg adds to the corrosive resistance of the rim [2].

2 mm

110 µm

50 µm