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The rapid industrial development calls for alloys that possess higher comprehensive properties. In this study, the effect of micro-alloying La addition on the precipitation behavior during artificial aging as well as the mechanical properties and electrical conductivity of Al-Mg-Si alloys were investigated by thermal analysis, microstructural characterizations and properties tests. The results demonstrated that micro-alloying La addition does not change the whole precipitation sequence during the artificial aging of Al-Mg-Si alloys as well as the atomic structure of the precipitates. However, the higher La-vacancy binding energy as well as the strong La-Si and La-Mg interactions can decrease the solubility of Si and Mg in the Al matrix and the β″ precipitation activation energy from 89.9 to 76.7 kJ/mol, leading to the improvement of the strength and electrical conductivity of Al-Mg-Si alloys simultaneously. The microstructural features affecting the strength and electrical conductivity were theoretically discussed in terms of the La addition.

A population dynamics-cellular automaton (PD-CA) model is developed to describe the microstructure formation in an inoculated Al alloys. The model involves the dynamics behaviors of the inoculated particles and the nucleation, initial spherical growth of nuclei as well as the subsequent dendritic growth. The model was validated by using the experimental results for the Al-Cu alloys inoculated by Al–Ti–C refiner first, and then used to simulate the detailed solidification process in an inoculated Al–Cu alloy. The results indicate that the TiC is not stable in Al melt. The heterogeneous nucleation process consists of two stages: a very short initial stage dominated by the cooling rate and the later stage dominated by the number of the active TiC. It stops at the very moment the recalescence occurs. The average grains size d of the aluminum alloys inoculated by the Al–Ti–C refiner can be calculated by $$d(\upmu{\text{m}}) = \frac{{a \cdot \exp (t/60 \cdot \ln (C_{ 0} /w))}}{{(\nu_{\text{cool}} \cdot t)^{1/3} w^{1/3} }} + \frac{b \cdot \ln t}{{Q \cdot v_{\text{cool}}^{1/2} }}$$ where Q is the growth restriction factor, C0 (%) is the initial solutes composition, w (%) is the additive amount of Al–Ti–C refiner. t (min) is the holding temperature time since the Al–Ti–C refiner is added into the melt. a and b are the constants.

To investigate the effect of high-pressure water jet assistance on hard rock breakage by mechanical impact, a rate-dependent constitutive model was adopted to describe the mechanical behavior of the rock. Then, a numerical model of rock breakage was developed using the coupled smoothed particle hydrodynamics (SPH) and finite element method (FEM). The indenter and rock stress and rock breakage features were used to evaluate the assisted effect of the high-pressure water jet. The rock stress perturbation by water jet assistance was more intense than that by indenter impact alone, which could result in more microscopic damage in the hard rock. For the normal indenter and water jet impact velocities, the peak indenter stress could be reduced by more than 30%. As the distance between the indenter and water jet impact points increased from 0 to 12.5 mm, the peak indenter stress decreased accordingly from 71.6% to 14.7% compared with the indenter stress without water jet assistance, and it decreased with increasing distance. The influence rule of the bilateral water jets on rock breakage and indenter stress is analogous to the unilateral condition, but the enhanced degree of breakage performance with bilateral water jets is better than that of the unilateral water jet. The inclined angle of the water jet also has an important effect on the rock breakage performance, and the inclined angle in the range of 80° ~ 90° is better for hard rock breakage. The allowable intersection angle between the impact directions of the water jet and indenter is important and significant for retaining the structural integrity of the indenter.

An integrated model based on the population dynamics approach and the cellular automaton method has been developed to simulate the solidification process of the Al-Zn-Mg-Cu alloys. The nucleation, spherical growth/dissolving and dendritic growth of the α-Al nuclei/grains are taken into account. The model is validated by comparing with the experimental results firstly, and then is applied to calculate the details of the microstructure formation in Al-Zn-Mg-Cu alloys inoculated with Al-5Ti-1B master alloys. The effects of the size distribution of TiB2 and the solidification conditions on the grain size are investigated. At last, an empirical formula for predicting grain size has been put forward based on the numerical calculations. The formula gives the dependent relationship between the grain size, the cooling rate of melt, the additive amount of refiner, the composition of the solutes and the size distribution of TiB2 particles.

The effects of rare earth element on the microstructures, tensile properties and electrical properties of aluminum alloys have brought about widespread interesting in the last few decades. However, contradictory results are usually reported, and there is little research concerning the effect law of trace lanthanum (the addition is below 0.1 wt%) on the as-cast microstructures, electrical conductivity and the tensile properties of 8176 aluminum alloy which is one of the most widely used aluminum conductor alloy. In this work, solidification experiments were performed with 8176 aluminum alloy and the effects of lanthanum addition was investigated. The results demonstrated that the lanthanum addition can promote the refinement of the alpha Al grains, the modification of Al13Fe4 intermetallic phase. The elongation and electrical conductivity simultaneously enhance with lanthanum addition when the additive amount is less than 0.08%, while the elongation decreases when the additive amount reaches to 0.1% due to the formation of intermetallic phase. The enhancement of the elongation is mainly ascribed to the modification of Al13Fe4 intermetallic phase, the enhancement of the electrical conductivity is attributed to the reduction of solid solubility of Si and Fe elements in Al matrix. These results indicate that the addition of micro-alloying element lanthanum is a prospective method for simultaneously elevating the electrical conductivity and tensile properties of the 8176 aluminum alloy.

Copyright © 2014 Hongxiang Jiang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited., Rock breakage by coupled mechanical and hydraulic action has been developed over the past several decades, but theoretical study on rock fragmentation by mechanical tool with water pressure assistance was still lacking. The theoretical model of rock breakage by mechanical tool was developed based on the rock fracture mechanics and the solution of Boussinesq’s problem, and it could explain the process of rock fragmentation as well as predicating the peak reacting force. The theoretical model of rock breakage by coupled mechanical and hydraulic action was developed according to the superposition principle of intensity factors at the crack tip, and the reacting force of mechanical tool assisted by hydraulic action could be reduced obviously if the crack with a critical length could be produced by mechanical or hydraulic impact. The experimental results indicated that the peak reacting force could be reduced about 15% assisted by medium water pressure, and quick reduction of reacting force after peak value decreased the specific energy consumption of rock fragmentation by mechanical tool. The crack formation by mechanical or hydraulic impact was the prerequisite to improvement of the ability of combined breakage.

U svrhu istraživanja opterećenja reznih glava opremljenih vodenim mlazom razvijena je oprema za ispitivanje fragmentacije stijene pomoću rezne glave. Vodeni mlaz se tu upumpavao u središte konusnog šiljka (pick). Bez vodenog mlaza, karakteristični indeks reznog momenta i vlačne sile eksponencijalno se povećao s tlačnom čvrstoćom stijene. Nije primijećena jasna povezanost između karakterističnih indeksa reznog momenta i tlačne čvrstoće stijene u slučaju s vodenim mlazom, ali je učinak vodenog mlaza na vlačnu silu rezne glave bio relativno postojan. Rezni moment i vlačna sila su se smanjili za 20 % do 40 % kada je tlačna čvrstoća stijene bila niža od tlaka vodenog mlaza. Ipak, vodeni mlaz koji je pomogao u fragmentaciji stijene, bio je manje učinkovit kad je tlak vode bio slabiji od tlačne čvrstoće stijene. Omjer između tlaka vodenog mlaza i tlačne čvrstoće stijene može pomoći kod prepoznavanja učinkovitosti vodenog mlaza kod reznih glava za fragmentaciju stijene., A test bed for rock fragmentation by cutting head was developed to investigate the load of water jet-assisted cutting heads. In this test bed, water jet was pumped into the center of the conical pick. In the case without water jet, the characteristic index of the cutting torque and pulling force increased with the rock compressive strength exponentially. No obvious relationship was observed between the characteristic indexes of the cutting torque and the rock compressive strength for the case with water jet, but the effect of the water jet on the pulling force of the cutting head was relatively stable. The cutting torque and pulling force were decreased by 20 % to 40 % when the rock compressive strength was lower than the water jet pressure. However, the water jet that assisted in rock fragmentation was less effective when the water pressure was lower than the rock compressive strength. The ratio between water jet pressure and rock compressive strength can help recognize the efficiency of water jets for rock fragmentation by cutting head.

Continuous solidification experiments were carried out with Cu-Bi-Sn alloys under the effects of Electric Current Pulses (ECPs). A model describing the microstructure evolution was developed. The formation of the microstructure in the continuously solidified alloys was calculated. The calculations demonstrated that ECPs mainly affect the solidification process through changing the energy barrier for the nucleation of the minority phase droplets (MPDs). When the matrix liquid has a lower electric conductivity compared to the MPD, the ECPs lead to a decrease in the energy barrier for the nucleation of the MPDs which then promote the formation of a finely dispersed microstructure. When the matrix liquid has a higher electric conductivity compared to the MPD, the ECPs cause an increase in the energy barrier for the nucleation and lead to the formation of a phase segregated microstructure.

Gas-solid injectors are widely used feeding equipment in pneumatic conveying systems. The performance of a gas-solid injector has a significant influence on the type of application it can be employed for. To determine the key factors influencing the injection performance and address clogging problems in a gas-solid injector during a pneumatic conveying process, the particle trajectory model has been utilised as a means to perform simulations. In the particle trajectory model, the gas phase is treated as a continuous medium and the particle phase is treated as a dispersed phase. In this work, numerical and experimental studies were conducted for different nozzle positions in a gas-solid injector. A gas-solid injector test-bed was constructed based on the results of the simulations. The results show that the nozzle position is the key factor that affects the injection performance. The number of extrusive particles first increases and then decreases with the change in the nozzle position from left to right. Additionally, there is an optimum nozzle position that maximises the injection mass and minimises the number of particles remaining in the hopper. Based on the results of this work, the injection performance can be significantly increased and the clogging issues are effectively eliminated.