The only aluminum alloy series with all of the elements found in the carabiner is the 7xxx series in which 7075 is the most common. It is likely that the parts underwent a T6 heat
treatment to reach their peak age condition due the carabiners strength
requirements. An average microhardness of ten measurements wasfound to be 183.8 HV which is close to literature microhardness values of7075-T6 aluminum which are around 175 HV. The precipitate phase in7075 aluminum is MgZn2 but is too small to be resolved in the LOM orSEM. Black Diamond confirmed that the aluminum parts are 7075-T6 aluminum.
What is a Carabiner?Carabiners are a simple but eloquent device that can be used to support a person as well as their equipment during a climb. This $19 device can sustain tremendous forces and make the difference in a life or death situation. We have chosen to analyze the Black Diamond Rocklock Twistlock Carabiner due to its popularity and customer satisfaction.
The body and latch are comprised of a 7XXX series aluminum alloy and strengthened with MgZn2precipitates.
Additionally the aluminum parts have anodized surfaces.
The pin and the latch exhibited longitudinal and transverse directionality due to deformation processing.
The pin is made of an austenitic 3XX series stainlesssteel containing Ni, Cr, and Fe.
Metallographic Analysis of a Black Diamond Rocklock Twistlock CarabinerClass 3
Based on a rough density measurement and lack of magnetism, the pin was hypothesized to be austenitic stainless steel. It was electrolytically etched for 30 seconds in 60% HNO3/40% H2O using a voltage of 0.6 DC. Micrographs of the longitudinal direction show ghost lines flowing in the direction of deformation that most likely result from drawing or extruding the original part.
EDS spectra of the pin revealed that the primary elements were iron, chromium, and nickel, in which nickel is an austenitic stabilizer. The EDS spectra did not show any manganese, which led to the conclusion that the part was 300 series stainless steel not 200.
The SEM and LOM revealed there is also aluminum throughout the sample, which is most likely due to the polishing process. Stainless steel was most likely chosen for the pin because it has good wear resistance and the pin experiences friction when the carabiner is
opened and closed. Black Diamond confirmed that the pin is 305 stainless steel.
For light optical microscopy, the aluminum samples were etched in Kellers Reagent for 45 seconds. The grains along the longitudinal direction exhibited directionality that was most likely a result of preparing the rod stock through extrusion or drawing. The transverse direction also showed grain elongation that was most likely a result of cold forging. The dark particles in the micrographs are the intermetallics that were analyzed in the SEM.
References:Mills, Kathleen. ASM Handbook. Volume 9. Metallography and Microstructures.
Materials Park, OH: ASM International, 1985. Print.
SEM particle mapping showed an even dispersion of zinc within an aluminum matrix for the body, latch and locking mechanism of the carabiner. Two uniquetypes of particles were found and analyzed using
EDS. One was determined be an intermetallic rich inmagnesium and silicon and the other was concluded to be an intermetallic rich in iron, copper, and aluminum. The SEM also revealed that
the surface of the aluminum parts were anodized to create a decorative corrosion resistant finish.