Effects of 4 GPa Pressure Heat Treatment on Microstructure and Micro-Mechanical Properties of LC4 Aluminum Alloy

Abstract

Microstructure and micro-mechanical properties of LC4 aluminum alloy were studied before and after treating the samples at 4GPa pressure. The hardness, elastic modulus and plastic deformation were measured by nanoindenter and the microstructure of the LC4 aluminum alloy was observed by metalloscope and scanning electron microscope. The results show that the microstructure of the LC4 aluminum alloy can be refined and compacted after 4GPa pressure treatment. The micro-mechanical properties of LC4 aluminum alloy can be improved effectively. (doi:10.2320/matertrans.M2013040) The materials to be test were LC4 aluminum alloys (Al 89.02%, Zn 6.13%, Mg 2.26% ,C u 1.65%, Cr 0.16% ,M n 0.34%, Fe 0.32%, Si 0.12%. mass fraction, %). The aluminum alloy rods were annealed into a KLX-13A programmable Nabertherm furnace at 475°C for 60min and furnace-cooled to room temperature. High-pressure experi- ments were performed on the CS-IIB type six-anvil high- pressure equipment. The annealing samples were pressurized to 4GPa and heated to 470°C for 60min. Then the pressure was released until the samples were cooled to room temperature with the cooling circulating water flow rate is 1.5L/min. The samples after high pressure treatment were cut into ¯8mm© 5mm size specimens, the micro-mechan- ical experiments were carried out on a triboindenter nano- mechanical test instrument. Berkovich-type indenter with curvature radius of 150nm was chosen to measure the hardness and elastic modulus. The loading and displacement detectability of this testing system were 50nN and 0.01nm, respectively. In which the maximum applied load was1000µN and kept at this load for 10s, the loading and unloading rates were 100µN·s ¹1 . The data was obtained by averaging the test values of repeated 5 measurements. The changing values of the specimen's hardness and elastic modulus with different indenting depth can be obtained by continuous loading and unloading on a certain area of the sample's surface and kept at this load for 1s. The microstructures of the samples were observed on the Axiovert 200MAT metalloscope and S-3400N Scanning electron microscope (SEM-BSE). 3. Results and Discussion