Influence of grain refiner addition and heat treatment on the mechanical properties of Al-Si alloy
In the present investigation, an attempt is made to study the effect of addition of grain refinement on Al-Si alloy, when it is subjected to the combined grain refiner addition (Al-5T-1B) and subjected to mechanical vibration and heat treatment. The material is tested for hardness property and dry sliding wear properties. The results of the present investigation indicate that there is a considerable improvement in the hardness valves, microstructure and resistance for wear.
Effects of T6 heat treatment on the microstructure, tensile properties, and fracture behavior of the modified A356 alloys
Abstract It is known that heat treatment causes the spheroidization of eutectic silicon. This paper presents the influence of T6 heat treatment on the microstructures, tensile properties, and fracture behavior of the A356 alloys modified by mischmetal containing La and Ce elements. Microstructural analysis showed that the size of eutectic silicon particles was greatly reduced and the extent of speroidisation of Si particles was remarkably improved for the modified A356 alloys. Comparison between the unmodified and modified alloys suggested that the values of mean diameter, roundness, and aspect ration of eutectic silicon particles were decreased by 48.10–56.85%, 49.55–54.52%, and 13.36–30.17%, respectively. The tensile properties of the modified A356 alloys can be enhanced, especially the ductility. These could be associated with the decrease of secondary dendrite arm spacing, spheroidization of fine eutectic silicon and precipitation hardening. Scanning electron microscopy (SEM) examination indicated that the ductile fracture mechanism was responsible for the modified alloys due to the existence of a couple of fine and uniformly distributed dimples. And the eutectic silicon particles and RE-containing intermetallic compounds provide the weak locations during the fracture process.
Experimental investigation of the geotechnical properties and microstructure of lime-stabilized saline soils under freeze-thaw cycling
Abstract The Song-Nen Plain in northeastern China holds one of the three largest expanses of soda saline-alkali soil in the world. Due to its disadvantageous geotechnical properties, the saline soil in this area is unable to meet the needs of construction projects. This study evaluates the stabilizing effect of adding lime to such soils. Specifically, it investigates how the physicochemical and mechanical properties and microstructure of soda saline-alkali soil are altered by lime and how these changes are affected by both freeze-thaw cycling and the duration of curing. The results reveal that adding lime to saline soil transforms clay particles into sand and silt particles and causes the pore size distribution (PSD) to become bimodal, with small-pore and macropore populations. An increase in lime content leads to an increase in the unconfined compressive strength (UCS) but a gradual decrease in both the cation exchange capacity (CEC) and plastic index. Freeze-thaw cycles break up coarse particles and aggregate finer particles, increasing the diameter of macropores and decreasing the USC; however, the effect on specimens with >9% lime is negligible. It is further shown that the geotechnical properties of the soil change immediately after the addition of lime, indicating that the cation exchange reaction takes place very quickly. Furthermore, the pozzolanic reaction leads to an increase in the percentage of sand-sized particles and a decrease in porosity after 28 days of curing. Overall, these results indicate that it is feasible to use lime to improve the engineering properties of soda saline-alkali soil in this area.