A Corrosion Analysis of Cree® Fixtures

Abstract: The aluminum castings used for Cree luminaires, in conjunction with the DeltaGuard™ coating system, have already been subjected to corrosion testing and reported on in a White Paper published May 2008. The results of that study showed that after 5,000 hours in a salt fog cabinet, the castings passed the corrosion test with a rating of 4, as per ASTM Standard 1694 D, procedure A. After the 2008 White Paper was published, Cree was questioned whether other parts of Cree luminaires exposed to the environment would provide as good of results as the castings did. In particular, the concern focused on the extruded aluminum heat sinks, and the patented NanoOptics™ used to refract light from each LED. The premise of this paper is to show that not only will the complete Cree fixture survive a 5,000 hour salt fog test; the light output will not be compromised. Based on this study, it is concluded that the extruded aluminum alloys met or exceeded the corrosion resistance of the castings, and the light output of the Cree fixture suffered no negative consequences after being exposed to 5,000 hours in a salt fog cabinet.

A Corrosion Analysis of Aluminum Alloys and Coatings

Abstract: As worldwide trade increases, a wide variety of aluminum castings and coatings have been introduced into the lighting industry. Often, inexpensive products have been installed with less than acceptable corrosion results. In response, some agencies/governments are trying to regulate the type of aluminum alloy that can be used. This type of alloy is generally extremely low in copper, and as such is much more resistant to corrosion than the more traditional alloys used. The low copper aluminum alloy standard most often referenced is the LM6 classification of the BS 1490 standard. Unfortunately, this type of alloy is often more expensive, more difficult to cast or machine, and may not provide the same structural strength (too ductile) as other available alloys. The premise of this paper is to show that it is not as advantageous to regulate the use of a specific alloy to control corrosion, as it is to regulate that the combination of alloy and coating meet specified corrosion test requirements. Therefore, this paper reviews the results of a 5,000 hour salt fog test performed on common die cast alloys that range in copper content, with various coatings applied. Based on this study, it is concluded that aluminum alloys with a higher copper content than what is permitted by LM6, can show a far superior corrosion resistance when the proper coatings are employed. These alloys also provide the greater structural integrity and tensile strength needed for many lighting applications.