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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.

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.

To investigate the rock fragmentation mechanism and its influence factors under discontinuous water-jet impact, the fluid-structure coupled smoothed particle hydrodynamics (SPH) and finite element analysis (FEA) was used to simulate the rock fragmentation process. A rate-dependent constitutive model was adopted to describe the mechanical behavior of rock, and the shock equation of state was used to simulate the water-jet. The rock fragmentation statuses under continuous and discontinuous water-jet impact were simulated and compared under the same initial impact energy, and the rock failure mechanisms, such as the crushing zone and crack formation, were investigated through the elements of pressure and stresses as a function of time. The effects of water-liquids distance and length on rock fragmentation by the discontinuous water-jet were also analyzed. With the same energy, the rock fragmentation performance of the discontinuous water-jet was better than that of the continuous water-jet. The failure of the rock crushing zone was mainly caused by plastic behavior; however, the crack propagation presented brittle failure. The “water cushioning effect” would appear when the water-liquids distance was too small, which restricted the impact effect on rock fragmentation. Discontinuous water-jet with a shorter water-liquid length would result in a deeper crushing zone and volume fragmentation of rock.

To investigate the rock fragmentation and its influence factors under the impact load of water jet, a numerical method which coupled finite element method (FEM) with smoothed particle hydrodynamics (SPH) was adopted to simulate the rock fragmentation process by water jet. Linear and shock equations of state were applied to describe the dynamic characteristics of rock and water, respectively, while the maximum principal stress criterion was used for the rock failure detection. The dynamic stresses at the selected element containing points in rock are computed as a function of time under the impact load of water jet. The influences of the factors of boundary condition, impact velocity, confining pressure, and structure plane on rock dynamic fragmentation are discussed.

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.

For so much error caused in drum’s cutting specific energy consumption calculation when using sharp cutter’s cutting specific energy formula, the drum’s torque mathematical model and cutting specific energy consumption mathematical model which took Goktan’s conical pick cutting mathematical model as basic was established refer to the drum cutting curves of the sequence drum, the punnett square drum, the aberrance 1 drum and the aberrance 2 drum. The tests of four type drums and four sequence drums which installed different cone angles were carried out in cutting test bed. The results indicate that: the similarity of calculate result and test result can support the theoretical research;cutting torque and cutting specific energy consumption rise with the cone angle increasing; the minimum torque and cutting specific energy consumption was produced by 2-starts vane punnett square drum, 3-tarts vane aberrance drums produced more larger torque and cutting specific energy consumption；Using punnett square drum in coal cutting can reduce cutting specific energy consumption, but 3-tarts vane aberrance drums have no advantage compared with 2-tarts vane sequence drum in reducing cutting specific energy consumption. DOI: http://dx.doi.org/10.11591/telkomnika.v11i7.2869