The influence of natural ageing on the artificial ageing response of Al-Si-Cu-Mg casting alloys

The T6 heat treatment is commonly used to increase the strength of gravity cast Al-Si components containingCu and/or Mg. The artificial ageing response is known to be affected by the thermal history, such as solutiontreatment, quench rate, natural ageing and heating rate to the artificial ageing temperature. The influence ofnatural ageing on the artificial ageing response was investigated for three alloys; Al-8Si-0.4Mg, Al-7Si-3Cu andAl-8Si-3Cu-0.4Mg. Natural ageing had a strong influence on the ageing response of the Al-Si-Mg alloy in theunderaged condition and the strength increase was strongly reduced. Despite this, the time to peak yieldstrength as well as its magnitude were not strongly affected by natural ageing. No clear influence of naturalageing was observed for the Al-Si-Cu alloy. For the Al-Si-Cu-Mg alloy the ageing response seems to depend onthe natural ageing time. Natural ageing of 3 weeks shifted the peak yield strength to shorter ageing times andits magnitude was decreased a little compared to direct ageing after quench. Natural ageing of 1 day gave theleast beneficial properties after artificial ageing

The influence of Fe and Mn content and cooling rate on the microstructure and mechanical properties of A380-die casting alloys

In the present investigation, the microstructure and tensile properties of aluminium die-cast alloys, based on A380, are studied in details as a function of the iron and manganese content and solidification rate. One set of experiments was designed to examine the ?solely? effect of Fe content, which varied from 0.1 up to 1.6 wt % and another set with manganese additions, Mn:Fe ~ 1:2. Three solidification rates corresponding to ~ 10, 25 and 60 ?m in secondary dendrite arm spacing, SDAS, respectively were employed by using the unique gradient solidification technique. Microstructure analysis reveals that at relatively high cooling rates and iron levels, the iron-rich precipitates are suppressed to some extent and the strength is maintained at high levels, but the ductility is gradually decreased. The amount of iron-rich intermetallics does not appear to influence the size and area fraction of porosity and consequently the result suggests that tensile properties have not been adversely affected by porosity level. These results offer additional insight into commonly discussed microstructure features and their role in the determination of the quality and soundness of Al-Si cast alloys

Use of simulation to predict microstructure and mechanical properties in an as-cast aluminium cylinder head comparison - with experiments

This contribution aims to validate a newly developed addon module to a commercial simulation software, which enables the prediction of the microstructure and mechanical properties of aluminium cast alloys under different casting conditions. The simulation of the casting process and the resulting microstructure and mechanical properties, permits a reduction of experimental testing and providing the best solution of process and material selections, thereby making the design and development process more cost efficient. The simulation results are compared with the investigation of the microstructural and mechanical behaviours of an As-Cast Aluminium cylinder head processed by semi permanent gravity die casting. It is demonstrated that the predictions made by the simulations are comparable to the experimental results. In order to further enhance the quality of the simulation tool, it is of significance to gain more experience from comparisons with complex castings of different aluminium alloys, where the microstructure as well as the mechanical properties are carefully evaluated

Variations In Microstructure And 12 Mechanical Propreties Of Cast Aluminum EN AC 43100 Alloy

The microstructure and mechanical properties of a gravity die and sand cast Al-10%Si-0.4%Mg alloy, which is one of the most important and frequently used industrial casting alloys, were examined. Tensile test samples were prepared from fan blades and sectioned through three positions which experienced different cooling rates. Furthermore, the inherent strength potential of the alloy was revealed by producing homogeneous and well fed specimens with a variety of microstructural coarseness, low content of oxide films and micro-porosity defects, solidified in a laboratory environment by gradient solidification technology. The solidification behaviour of the alloy was characterized by thermal analysis. By means of cooling curves, the solidification time and evolution of the microstructure was recorded. The relation between the microstructure and the mechanical properties was also assessed by using quality index-strength charts developed for the alloy. This study shows that the microstructural features, especially the ironrich needles denoted as ?-Al5FeSi, and mechanical properties are markedly affected by the different processing routes. The solidification rate exerts a significant effect on the coarseness of the microstructure and the intermetallic compounds that evolve during solidification, and this directly influences the tensile properties

Wnt/β-Catenin Signaling Pathway Is a Direct Enhancer of Thyroid Transcription Factor-1 in Human Papillary Thyroid Carcinoma Cells

The Wnt/β-catenin signaling pathway is involved in the normal development of thyroid gland, but its disregulation provokes the appearance of several types of cancers, including papillary thyroid carcinomas (PTC) which are the most common thyroid tumours. The follow-up of PTC patients is based on the monitoring of serum thyroglobulin levels which is regulated by the thyroid transcription factor 1 (TTF-1): a tissue-specific transcription factor essential for the differentiation of the thyroid. We investigated whether the Wnt/β-catenin pathway might regulate TTF-1 expression in a human PTC model and examined the molecular mechanisms underlying this regulation. Immunofluorescence analysis, real time RT-PCR and Western blot studies revealed that TTF-1 as well as the major Wnt pathway components are co-expressed in TPC-1 cells and human PTC tumours. Knocking-down the Wnt/β-catenin components by siRNAs inhibited both TTF-1 transcript and protein expression, while mimicking the activation of Wnt signaling by lithium chloride induced TTF-1 gene and protein expression. Functional promoter studies and ChIP analysis showed that the Wnt/β-catenin pathway exerts its effect by means of the binding of β-catenin to TCF/LEF transcription factors on the level of an active TCF/LEF response element at [−798, −792 bp] in TTF-1 promoter. In conclusion, we demonstrated that the Wnt/β-catenin pathway is a direct and forward driver of the TTF-1 expression. The localization of TCF-4 and TTF-1 in the same area of PTC tissues might be of clinical relevance, and justifies further examination of these factors in the papillary thyroid cancers follow-up

On the influence of quenching rate on the microstructural and mechanical properties of aluminium cast alloys A356 and A354

The impact of quench rate on the microstructural and mechanical behaviour is assessed in this paper. Two common commercial aluminium foundry alloys, A356 and A354, are investigated. Samples were produced by employing gradient solidification technology which generates uniformly and directionally solidified specimens with different microstructural coarsenesses. Generally, heat treatment is widely applied to strengthen the Al-Si-Cu-Mg cast alloys through precipitation hardening. Measurements of electrical conductivity have been conducted in order to indicate the sequences of precipitation formations. To optimise the precipitation hardening effect, it is essential to understand the quench sensitivity. It can be concluded that the quench rate significantly influences the mechanical properties; the tensile strength and strength coefficient are enhanced with an increase in quench rate. The ductility instead increases with a reduced quench rate, which might be due to the more ductile \u3b1-Al matrix with corresponding coarsening and reduced level of hardening precipitates

HighT – Development of High Technology Castings

Enhanced production and post production techniques and materials optimisation, performed in the project “HighT – Development of High-Technology Castings, have enabled production of cast components with improved mechanical and wear properties as well as lower weight and less variation in properties. Within the project three important fields have been studied; High-Strength Cast Iron, Lightweight Components and Combining materials though casting. The results from the work with High-Strength Cast Iron have enabled production of solution hardened castings with both thin and tick wall sections. By enhanced production of molds and cores, the spread in component properties has also been reduced. Within the work regarding Lightweigt Components, the microstucure and pore content levels have been related to mechanical strength. Also, methods for modelling of residual stresses have been proposed. By combining casting simulation and casting trials, the work related to New Technologies has resulted in an technoque for combining different materials thorugh casting. With this technique, it is possible to produce components with better wear properties than found in today’s wear parts