Thermal Profiles and Fraction Solid of Aluminium 7075 at Different Cooling Rate Conditions

Abstract

Abstracts:In order to determine suitable processing conditions for semi-solid aluminium 7075 thermal analysis (TA) was performed in order to obtain the relationship between fraction solid and temperature. During experimental work, the alloy was heated to 750°C by resistance heated box furnace and solidified at various cooling rates. Cooling curves for the metal were recorded with two thermocouples, one at the centre of the melt volume and one beside the containing crucible wall. A specially designed chamber with kaowool blanket was used to achieve the slowest cooling rate. The faster cooling rate was achieved with the crucible in open atmosphere with a set air flow rate over the crucible. A Data Acquisition (DAQ) system controlled by LabVIEW software was used to record the temperature-time profiles. From these cooling curves, the phase change at any corresponding time and temperature was estimated. The temperature difference between centre and wall of crucible was used to determine dendritic coherency point (DCP). Results show that, the slowest cooling rate with the kaowool blanket was at 0.03°C/s. An intermediate cooling rate of 0.21°C/s was achieved by leaving the melt to cool without kaowool blanket or forced air flow, and the fastest cooling rate was 0.43°C/s. The change in cooling rate altered the temperatures at which phase changes occurred, including those for eutectic and solidus. It was found that for lower the cooling rates that the DCP occurred at lower temperatures. The DCP for the cooling rate of 0.03°C/s was found to be 574°C (corresponding to 0.85 fraction solid) whereas the DCP for 0.43°C/s was found to be 623°C (corresponding to 0.55 fraction solid).

Direct Thermal Method of Aluminium 7075

“…Schematic diagram for DTM apparatus is presented in Fig.1 as follows: The semi-solid temperature range of 7075 alloy is quoted with the different solidus and liquidus temperatures depending on the source of reference. In one previous work this range was reported as 472.8 °C to 636.7 °C [22]. Fig.…”

Removal of Tramp Elements within 7075 Alloy by Super-Gravity Aided Rheorefining Method

“…The increase of separation temperature will increase the amount of liquid phase and improve its flowability, which will lead to the increase of the filtrate amount. According to the study of ahmad and Cho, the solid fractions corresponding to each temperature in this work are 0.8 (609 °C ), 0.72 (617 °C ), 0.6 (625 °C ) [19,27]. The weight ratio of the residual accounting for the total weight is close to the theoretical solid fraction at the gravity coefficient of 1000 G. Thus, it is proved that the solid/liquid separation ratio with 1000 G is close to the theoretical value of solid/liquid fraction at different experimental temperatures.…”

“…The experimental conditions are shown in Table 2. The range of the semi-solid temperature of 7075 was determined to be 475-640 • C [19,27], the separation temperatures in this study were selected as 609 • C, 617 • C and 625 • C. And the gravity coefficients were selected as 400 G, 700 G, 1000 G. The gravity coefficient was calculated as the ratio of super-gravitational acceleration to gravitational acceleration via Equation (1) [28]. Where G is the gravity coefficient, N is the rotating speed of the centrifugal (r/min), R the distance from the centrifugal axis to the center of sample, R = 0.25 m, g = 9.8 m/s 2 .…”

Effect of Process Parameters of Backward Extrusion by Servo Press on Purification of A7075 Alloy under the Semisolid Condition

“…For the backward extrusion temperature of 620 C, the solid fraction was about 60% according to the temperature-solid fraction curve, 10) which is neither too low nor too high. It is known as the moderate value of the solid fraction according to the results of backward extrusion at 620 C. Thus, it was con rmed that the backward extrusion temperature affects the puri cation of aluminium and too limited in this study to achieve a higher purity of aluminium in the puri cation of A7075 alloy.…”

“…13. 10) After backward extrusion at 610 C, the weight percentage of puri ed aluminium was reduced and the puri ed aluminium was not distributed homogeneously in all the grains in the unextruded part. This was caused by the higher solid fraction due to the low temperature, and the tramp elements were incorporated in the solid puri ed phase.…”