Simulation of asperity plowing in an atomic force microscope. Part II: Plowing of aluminum alloys

Abstract

In this second part, we present results of plowing tests on three commercial aluminum alloys using the atomic force microscope technique presented in Part I. Pure (99.99%) aluminum, 5182-O, and 7150-T6 were chosen as substrates because of their different material properties. These properties create different tribological conditions in processes such as rolling, forging, and extrusion where a metal workpiece flows plastically due to contact with a hard tool surface having many asperities. In the present technique, a single plow track was generated with a sharp diamond indentor which simulated a single tool asperity. A series of plow tracks was thus generated on each substrate surface over a range of plowing speeds and normal forces. The resulting plow track geometries and plowing forces were measured for input to the theoretical model presented in Part I. The model was used to predict material flow stress as a function of normal force as well as friction factors at the different indentor faces. The flow stress predictions from the model w ere compared with flow stress measurements from Vickers microhardness tests of each material. This helped to reveal possible scale effects and highlight tribological phenomena that are peculiar to plowing. The friction factor was found to be strongly dependent on the ratio of the measured ridge height to the depth of cut. This ratio is known to depend upon material properties such as strain hardening, elastic recovery, densification beneath the indentor, etc., that are not captured within the theoretical framework. Results from some plowing tests with a blunt indentor are reported and comparisons are made with those with the sharp indentor.