Temperature Effects on the Tensile Properties of Precipitation-Hardened Al-Mg-Cu-Si Alloys
Because the mechanical performance of precipitation-hardened alloys can be significantly altered with temperature changes, understanding and predicting the effects of temperatures on various mechanical properties for these alloys are important. In the present work, an analytical model has been developed to predict the elastic modulus, the yield stress, the failure stress, and the failure strain taking into consideration the effect of temperatures for precipitation-hardenable Al-Mg-Cu-Si Alloys (Al-A319 alloys). In addition, other important mechanical properties of Al-A319 alloys including the strain hardening exponent, the strength coefficient, and the ductility parameter can be estimated using the current model. It is demonstrated that the prediction results based on the proposed model are in good agreement with those obtained experimentally in Al-A319 alloys in the as-cast condition and after W and T7 heat treatments.
Temperature effects on the tensile properties of cast and heat treated aluminum alloy A319
Abstract In this work, the tensile properties and ductility of an Al-A319 alloy were investigated as a function of temperature and heat treatment. Tensile testing was carried out at temperatures ranging from −90 to 400 °C for the alloy in (a) the as-cast condition, (b) after solid solution at 485 °C (T4) and (c) after solid solution followed by ageing at 230 °C (T7). It was found that the alloy tensile strength was improved by heat treating from 195 MPa in the as-cast condition to 305 MPa in the T7 condition. Nevertheless, the alloy elongation was relatively poor, in the 2–3% all the way to temperatures in the neighborhood of 300 °C. The low alloy ductility was found to be related to internal damage dominated by cracking of intermetallic α-Al 15 (Mn,Fe) 3 Si 2 and θ-Al 2 Cu particles including silicon. Heat treating was found to increase the work hardening exponent, n in the σ  =  Kɛ n expression from 0.23 to almost 0.29. Moreover, it was found that n was not severely affected by temperature for temperatures below 200 °C. However, temperatures beyond 200 °C lead to appreciable reductions and overlapping in the magnitudes of n when compared with the as-cast condition. In turn, this indicated that above 200 °C, the work hardening properties of alloy A319 imparted by heat treating tend to dissipate. Apparently, bulk precipitate coarsening coupled with alloy softening mechanisms become active and they are dominant at temperatures above 300 °C. Moreover, the fraction of cracked particles was found to increase with temperature in this temperature regime. Weibull statistics and the probability of particle cracking indicated that at temperatures below 300 °C, damage accumulation by particle cracking is the dominant mode of fracture as indicated by the slope, m  = 3 of the linear Weibull plot. Depending on the alloy condition, critical particle stresses for cracking of 0.5–3 GPa were predicted using Weibull statistics.
Influence of pressure and fluidization velocity on the hydrodynamics of a fluidized bed containing horizontal tubes
Abstract An experimental investigation of the influence of horizontal tubes on the bubble behaviour and through-flow velocity of gas inside bubbles was carried out and the influence of pressure and fluidization velocity was studied. The visible bubble flow rate and the gas velocity through the bubbles were measured simultaneously in a pressurized fluidized bed, using capacitance and Pitot-static pressures probes respectively. Silica sand with a mean particle diameter of 0.7 mm was fluidized at pressures between 01. and 1.6 MPa, in a bed of 0.2 × 0.3 m cross-section. Six different horizontal tube configurations were used and comparisons were made with results obtained in the same bed operated without tubes. The results from the bed with tubes show that the influence of pressure and fluidization velocity is basically the same as in the bed without tubes; an increase in pressure and fluidization velocity increases the bubble activity. At low excess gas velocities, the influence of immersed tubes on the bubble behaviour is less pronounced than at high excess gas velocities. Measurements and visual observations show that a small tube pitch gives a more uniform distribution of the visible bubble flow over the bed cross-section. At a combination of high pressure, high excess gas velocity and a large tube pitch, a preferred bubble path was observed in the centre of the bed cross-section. The pressure probe measurements show that the through-flow velocity of gas inside the bubbles is in most cases higher when tubes are present in the bed. The through-flow velocity consistently decreases with increasing pressure in the bed without tubes. The tendency is largely the same at a low excess gas velocity when tubes are present, but at a high excess gas velocity the through-flow velocity first decreases and then increases as the pressure is increased.