Tribological Evaluation of Various Aluminum Alloys in Lubricant/Refrigerant Mixtures

Abstract

The tribological characteristics of various aluminum alloys, aluminum composites and some surface treated aluminum are evaluated in lubricant/refrigerant mixtures. All of these evaluations are based upon a specimen testing program using a high pressure tribometer (HPT). This research program mainly consists of two parts. The first part of this study is mainly focused on materials screening of various aluminum alloys/steel contact pairs lubricated by polyolesterlR134a and PAGIR134a lubricant/refrigerant (LIR) mixtures. In this study, various aluminum alloys are tested under the same environmental and operating conditions in order to compare their wear resistance. The results show that the lowest wear is obtained with the 390 Die Cast alloy. This alloy has the largest amount of silicon content and the highest bulk hardness. The results also show that, in general, the amount of wear decreases as the amount of silicon content in AI-Si alloys increases. Better wear resistance is also achieved if the amount of copper and bismuth are increased. Conventional anodizing does not improve the wear resistance of the 356 aluminum alloy under concentrated contacts. Hard anodizing and a SiC-AI composite provide very good wear resistance. However, they cause increased wear on the counterface by abrasion due to the rough, hard, surfaces generated by hard anodizing processes and the hard SiC particles. From the wear results obtained, the Ester/R134a mixtures consistently provide better protection of the aluminum alloys compared to the PAG/R134a mixtures. If sufficient amounts of R134a exists in the LlR mixture, extensive surface fatigue on 356 aluminum is observed. In the second part, two AI-Si alloys (356-T61 and 390-T61), widely used in critical components of refrigerant compressors, are examined fortheir friction and wear behavior in different LIR mixtures. The LIR mixtures tested include ester and PAG lubricants with R134a, mineral and alkylbenzene lubricants with R22, R407C and R410A, as well as an ester lubricant with both R407C and R41OA. Based on the wear data obtained, the capped P AG seems to be a better lubricant for 356 alloy than the uncapped PAG. However, the lubricity of the PAG's is about the same with the 390 alloy. When the ester lubricant is used, the wear on each alloy is about the same in R134a, R407C, R410A and air environments. There is no significant difference in lubricity of mineral and alkylbenzene lubricants when used with R22 and its possible substitutes R407C and R410A.Air Conditioning and Refrigeration Center Project 4