Modeling and optimization of cooling slope process parameters for semi-solid casting of A356 Al alloy

Semi-solid processing （SSP） of A356 aluminum alloy was discussed via cooling slope （CS） method. The D-optimal design of experiment （DODE） was employed for experimental design and analysis of results. 38 random experiments obtained by software were carried out. In experimental stage, the molten aluminum alloy was poured on an inclined plate with different lengths of 100, 300 and 500 mm set at 30°, 45° and 60° of slope angles respectively. Three different pouring temperatures of 660, 680 and 700 ℃ were also used. After the casting process, the partial re-melting treatment was carried out at 590 ℃ for different isothermal time of 5, 8 or 12 min. The combined effect of these factors on globularity of the primary α（Al） crystals was investigated and optimized using DODE. The results indicated that the primary dendritic phase in the conventionally cast A356 alloy was transformed into a non-dendritic one in ingots cast over a cooling plate. The CS processed samples exhibited a globular structure only after re-heating to semi-solid region. The optimum values of pouring temperature, cooling length, slope angle and isothermal holding time were found to be 660 ℃, 360 mm, 48°, and 9 min, respectively. In this case, the globularity of primary crystals was obtained, about 0.91. The obtained model is highly significant with a correlation coefficient of 0.9860.

The characteristics of rill development and their effects on runoff and sediment yield under different slope gradients

Rill formation is the predominant erosion process in slope land in the Loess Plateau, China. This study was conducted to investigate rill erosion characteristics and their effects on runoff and sediment yielding processes under different slope gradients at a rate of 10°, 15°, 20° and 25° with rainfall intensity of 1.5 mm min-1 in a laboratory setting. Results revealed that mean rill depth and rill density has a positive interrelation to the slope gradient. To the contrary, width-depth ratio and distance of the longest rill to the top of the slope negatively related to slope gradient. All these suggested that increasing slope steepness could enhance rill headward erosion, vertical erosion and the fragmentation of the slope surface. Furthermore,total erosion tended to approach a stable maximum value with increasing slope, which implied that there is probably a threshold slope gradient where soil erosion begins to weaken. At the same time, the correlation analysis showed that there was a close connection between slope gradient and the variousindices of soil erosion: the correlation coefficients of slope gradient with maximal rill depth, number of rills and the distance of the longest rill from the top of the slope were 0.98, 0.97 and-0.98, respectively,indicating that slope gradient is the major factor of affecting the development of rills. Furthermore,runoff was not sensitive to slope gradient and rill formation in this study. Sediment concentration,however, is positively related to slope gradient and rill formation, the sediment concentrations increased rapidly after rill initiation, especially. These results may be essential for soil loss prediction.

The intensity of slope and fluvial processes after a catastrophic windthrow event in small catchments in the Tatra Mountains

Strong wind events frequently result in creating large areas of windthrow, which causes abrupt environmental changes. Bare soil surfaces within pits and root plates potentially expose soil to erosion. Absence of forest may alter the dynamics of water circulation. In this study we attempt to answer the question of whether extensive windthrows influence the magnitude of geomorphic processes in 6 small second-to third-order catchments with area ranging from 0.09 km^(2) to 0.8 km^(2). Three of the catchments were significantly affected by a windthrow which occurred in December 2013 in the Polish part of the Tatra Mountains, and the other three catchments were mostly forested and served as control catchments. We mapped the pits created by the windthrow and the linear scars created by salvage logging operations in search of any signs of erosion within them. We also mapped all post-windthrow landslides created in the windthrow-affected catchments. The impact of the windthrow on the fluvial system was investigated by measuring a set of channel characteristics and determining bedload transport intensity using painted tracers in all the windthrow-affected and control catchments. Both pits and linear scars created by harvesting tend to become overgrown by vegetation in the first several years after the windthrow. The only signs of erosion were observed in 10% of the pits located on convergent slopes. During the period from the windthrow event in 2013 until 2019, 5 very small(total area <100 m^(2)) shallow landslides were created. The mean distance of bedload transport was similar(t-test, p=0.05) in most of the windthrow-affected and control catchments. The mapping of channels revealed many cases of root plates fallen into a channel and pits created near a channel. A significant amount of woody debris delivered into the channels influenced the activity of fluvial processes by creating alternating zones of erosion and accumulation.

Three-dimensional analysis of the modified sloping cooling/shearing process

A self-designed setup of modified sloping cooling/shearing process was made to prepare the semisolid Al-3wt%Mg alloy. A three-dimensional simulation model was established for the analysis of preparing the semisolid Al-3wt%Mg alloy. Through simulation and experiment, it is shown that the sloping angle of the plate greatly affects temperature and velocity distributions, and the temperature and velocity of the alloy at the exit of the sloping plate increase with the increase of the sloping angle. The alloy temperature decreases linearly from the pouring mouth to the exit. The alloy temperature at the exit increases obviously with the increase of pouring temperature. To prepare the semisolid Al-3wt%Mg alloy with good quality, the sloping angle θ=45° is reasonable, and the pouring temperature is suggested to be designed above 650-660℃ but under 700℃.

Lithological indicators of discontinuities in mountain soils rich in calcium carbonate in the Polish Carpathians

Six soils located within the Polish Carpathians,developed on calcium carbonate–rich sedimentary parent materials and representing various reference groups,were investigated in order to detect the lithic discontinuity.We propose using a multidirectional approach to assess the lithic discontinuity in these soils,one that includes grain size distribution,geochemical composition,heavy mineral content and micromorphology,supported by a traditional soil survey.A further aim of this process was to identify the possible admixture of allochthonous material of aeolian origin.The studied soils presented lithic discontinuities mostly at the contact of underlying calcium carbonate–rich coarsegrained slope deposits with the overlaying colluvium layer having a lower content of rock fragments.The significant changes in grain size distribution,especially in the silt and sand content,as well as high Uniformity Values and partially,high Lithological Discontinuity Index values,confirmed the occurrence of a lithic discontinuity in all studied soils.High heterogeneity in the soil profiles was also confirmed by the distribution of the major oxides;however,their distribution did not clearly indicate the lithic discontinuity.The most visible distinctions were noted from CaO content,which resulted from the deposition of carbonate-free materials(aeolian silts)and their mixing with the calcium carbonate–rich parent material.Furthermore,the analysis of heavy mineral content confirmed the allochthonous origin of the upper(and in some cases also the middle)parts of all profiles,which was manifested by the presence of highly weathering-resistant minerals such as zircon,epidote and various types of garnets.The micromorphological features of some of the studied soils showed distinctiveness within the soil profile,manifested by changes in b-fabric pattern,the occurrence and distribution of secondary carbonate and the coarse and fine coarse and fine ratio.Based on the high content of silt within the upper and middle parts of the soils,the content of Hf and Zr,as well as the higher content of weathering-resistant minerals,admixture of aeolian silt could be considered in some of the studied soils,yet with weak character.However,the dominance of minerals typical for metamorphic and igneous rocks suggested that the supply of aeolian silt was associated with loess covers rather than local sedimentary material.

The role of tree uprooting in the transporting of sediment and mixing of soil in the Tatra Mountains

Tree uprooting is an important process which leads to many geomorphic consequences.Some of the most important are the transport of sediment and mixing of soil.The aim of this article is to make a detailed examination of the magnitude of sediment transport caused by an extreme windthrow event in three severely affected catchments.Also,a comparison is made of the windthrow event with a mass movement event in the aspect of the magnitude of sediment transport and soil mixing.The study was conducted in three second-to third-order catchments in the Tatra Mountains,where a strong foehn wind event caused extensive windthrow in 2013,and a high-magnitude rainfall event triggered mass movements in 2007.The volume of sediment uplifted by the uprooting event was calculated based on the mapping of root plates using high-resolution(0.04 m)aerial images and measurements of root plate volumes conducted in the field.The volume of sediment transported by shallow landslides was determined based on a Digital Elevation Model(DEM1-m resolution).Windthrows affected 34%,76%,and94%of the area of the investigated catchments.Most of the trees had fallen downslope.The direction of treefall was influenced by the slope aspect and steepness.Root plates and pits covered 1.3%,4.8%,and 5.4%of the area of the catchments.Sediment flux generated by the uprooting event,calculated for the entire area of each investigated catchment ranged from 8.1×10^(–4) to 9.9×10^(–3) m^(3) m^(–1) event^(–1).This was notably lower than the sediment flux generated by the mass movement event(also calculated for the entire area of each catchment),which was 1.8-6.1×10^(–2)m^(3) m^(–1) event^(–1).By contrast,uprooting affected a much larger area than the mass movement event,which underlines its significant role in the mixing of soil.

Slope Processes, Mass Movement and Soil Erosion： A Review

Soil erosion and land degradation are global problems and pose major issues in many countries. Both soil erosion and mass movement are two forms of land degradation and humans play important roles in these geomorphological processes. This paper reviews slope processes associated with mass movement and soil erosion and contributory factors, including physical and human agents. Acting together, these cause diverse geomorphological features. Slope processes are illustrated by reference to case studies from Brazil and UK. The causes and impacts of erosion are discussed, along with appropriate remedial bioengineering methods and the potential of the measures to prevent these types of environmental degradation. Although there are several agents of erosion, water is the most important one. Cultivation can promote soil erosion, due to ploughing and harvesting, which moves soil down slopes. Soil erosion and mass movement data would inform the viability of soil conservation practices. Integrated management of drainage basins offers a Dromising way forward for effective soil conservation and soil remedial bioengineering in Brazil and UK.