Functional and Environmental Advantage of Cleaning Ti5B1 Master Alloy

One of the greatest environmental goals for the aluminum alloys industry is generating higher quality products by introducing cleaner input materials while maintaining low production costs. A typical dilemma for the master alloy producers is the cleanness level of the master alloy since insoluble inclusions could serve as inoculants during the solidification process. In this work, commercial Ti5B1 master alloy is used for grain refinement of Al7Si4Cu aluminum alloy and compared with the cleaned master alloy that contained a lower amount of residual refractory oxides and salts. Metallography analysis was used for grain size measurement while Computer Aided Cooling Curve Analysis was used for assessment of the undercooling and heat release values. In all instances, specimens treated with the cleaned master alloy showed smaller grains in the final structure and lower undercooling values. The difference in released heat between liquidus and recalescence temperatures was about 25% in specimens where added 0.66 wt% of cleaned master alloys compared to specimens where the commercial master alloys were added. Using cleaner Ti5B1 master alloy with a higher number of TiAl3 and TiB2 particles improves its grain refinement efficiency and transmits fewer impurities in produced parts. Producing cleaner master alloy would be beneficial from economic and environmental aspects by increasing its value and service time of produced parts besides simplifying the recycling process at the end of parts life-cycle.This is the peer reviewed version of the paper: Mitrašinović, A., Tomić, M., 2021. Functional and Environmental Advantage of Cleaning Ti5B1 Master Alloy, International Journal of Precision Engineering and Manufacturing-Green Technology, [https://doi.org/10.1007/s40684-021-00339-2

Канадски модел за прелаз од идеје до иновације

Invited presentation at the conference "From an idea to innovation", held at the Serbian Academy of Sciences and Arts in Belgrade on 7 April 201

Quality improvement of secondary aluminum alloys

21st- century market restructuring showed that superior structural materials around the world threatened the eradication of the North American automotive sector. The value of the global secondary aluminum market is over 40 billion dollars and therefore secondary alloys will remain a key source of feedstock material in the automotive industry for many years to come. Along with commercial motivation, one of the greatest environmental goals for the secondary aluminum alloys industry is generating higher quality products with longer service time by introducing cleaner input materials with no increase in production costs. Quality improvement of the feedstock material inevitably results in the improvement of structural and mechanical properties of the final parts. Two refining methods and one new quality control tool will be presented. One refining method uses the fact that aluminum has lower vapor pressure than most unwanted elements and these elements would evaporate if the alloy is melted in a vacuum. The second method refers to master alloys used to reduce grain size in the final structure. Using cleaner TiSBl master alloy with a higher number of TiAI3 and TiB2 particles transmitted fewer impurities, resulted in finer structure and increased strength of produced parts. The ever - increasing sensitivity and accuracy of new sensors allow Computer- Aided Analysis to assess materials' properties at the beginning of the solidification process, immediately evaluate acquired data and correlate these results to the mechanical properties of the finished parts. Here, we assessed a portion of latent heat released during the formation of the primary aluminum crystals, detected dendrite coherency point, and determined grain size later to solidify the alloy. Secondary aluminum alloys will stay in the global market for a long time. With increased environmental restrictions and demands for a higher quality of structural materials, the solutions rest in an improvement of the refining processes and advancement in quality control methods. Here are given examples of how producing cleaner master alloys and treating aluminum alloys in a vacuum would be beneficial considering economic and environmental aspects by increasing parts value, service time, and mechanical properties while simplifying the recycling process at the end of parts lifecycle

Assessment of Grain Size and Grain Refinement Efficiency by Calculation of Released Heat Attributed to Formation of Primary Aluminum Crystals During Solidification of Al7Si4Cu Alloy

Assessing heat released only related to the formation of primary crystals provides results with a significantly higher sensitivity than a traditional assessment of undercooling value. In this work, two similar Ti5B1 master alloys (commercial and refined) are used for grain refinement of Al7Si4Cu aluminum alloy to assess narrow differences in heat release during primary crystallization. The heat released related to primary crystallization is 2.50 ± 0.03, 3.16 ± 0.12, and 7.92 kJ kg-1 for samples treated with the refined master alloys, commercial master alloys, and sample solidified without grain refinement, respectively. The acquired results showed that the suggested method is more efficient in comparison with traditional metallographic or undercooling methods for the assessment of grain refining efficiency with the potential to extend the suggested approach on a wide range of metallic structures where solidification occurs by eutectic-type primary crystallization characteristics

The effect of the refractory material on the phase transformation parameteres during forming of the Al-8wt%Si-3wt%Cu structure

Očvršćavanje legura aluminijuma se najčešće odvija u termootpornim oblogama sačinjenim ili od metala ili od oksida koji su stabilni na visokim temperaturama. Značajno različita toplotna provodljivost između metala i termootpornih oksida prouzrokuje očvršćavanje sa različitim brzinama hlađenja. U ovom radu smo formirali sekundarnu leguru Al-8wt%Si-3wt%Cu u kalupu od nerđajućeg čelika, tankozidnoj čaši od nerđajućeg čelika i debelozidnoj čaši od cirkonijum oksida. Tok formiranja očvrsle strukture je praćen zaronjenim termoparovima koji su omogućili kompjutersku analizu krive hlađenja. Parametri na koje je brzina hlađenja imala najznačajniji uticaj su vrednosti pothlađenja formiranja primarnih kristala aluminijuma, vreme rasta primarnih kristala aluminijuma i ukupno vreme očvršćavanja od pojave prvih čvrstih kristala do formiranja potpuno očvrsle strukture. Al-8wt%Si-3wt%Cu legura aluminijuma formirana u metalnim kalupima ima manju veličinu zrna i posledočno veću zateznu čvrstoću, manju makroporoznost i manje hrapavu površinu od legure formirane u oblogama od termootpornih oksida. Ispitivane termootporne obloge su uticale na formiranje tri osnovna mikrokonstituenta u Al-8wt%Si-3wt%Cu leguri u različitim vremenskim intervalima, što je dovelo do formiranja različite mikrostrukture, gde odluka o izboru materijala termootporne obloge zavisi od isplativosti celokupnog procesa, zahtevanog kvaliteta spoljnih površina i zahtevane minimalne čvrstoće konačnog proizvoda.Solidification of the aluminum alloys takes place in heat-resistant refractory materials made of either metal or oxides that are stable at high temperatures. The significantly different thermal conductivities between metals and heat-resistant oxides cause solidification with significantly different cooling rates. In this work, we formed a secondary Al-8wt%Si-3wt%Cu alloy in a stainless steel mould, a thin-walled stainless steel cup, and a thick-walled zirconium oxide cup. The course of the formation of the solidified structure was monitored by immersed thermocouples, which enabled the computer analysis of the cooling curves. The parameters on which the cooling rate had the most significant influence are the undercooling values of the formation of primary aluminum crystals, the time of the growth of primary aluminum crystals and the total solidification time from the formation of the first solid crystals to the formation of a fully solidified structure. The Al-8wt%Si-3wt%Cu aluminum alloy formed in metal mould has a smaller grain size and consequently higher tensile strength, lower macro-porosity and less rough surface than the alloy formed in refractory oxide coatings. The examined heat-resistant refractory material influenced the formation of three basic micro-constituents in the Al-8wt%Si-3wt%Cu alloy in different time intervals, which led to the formation of a different microstructure, where the decision on the choice of material for the heat-resistant refractory material depends on the profitability of the entire process, the required quality of the external surfaces and required minimum strength of the final product

Modeling of Impurities Evaporation Reaction Order in Aluminum Alloys by the Parametric Fitting of the Logistic Function

Advancements in computer capabilities enable predicting process outcomes that earlier could only be assessed after post-process analyses. In aerospace and automotive industries it is important to predict parts properties before their formation from liquid alloys. In this work, the logistic function was used to predict the evaporation rates of the most detrimental impurities, if the temperature of the liquid aluminum alloy was known. Then, parameters of the logistic function were used to determine the transition points where the reaction order was changing. Samples were heated to 610 °C, 660 °C, 710 °C, and 760 °C for one hour, after which the chemical analyses were performed and evaporation rates were calculated for Cd, Hg, Pb and Zn elements. The pressure inside the encapsulated area was maintained at 0.97 kPa. Whereas parameters that define the evaporation rate increase with the temperature increase, the maximum evaporation rates were deduced from the experimental data and fitted into the logistic function. The elemental evaporation in liquid-aluminum alloys is the best defined by the logistic function, since transitions from the first to zero-order-governed evaporation reactions have nonsymmetrical evaporation rate slopes between the lowest and the highest evaporation rate point

Monitoring the amount of formed solid phase in aluminum alloy under free cooling conditions

Jedan od najefikasnijih načina za buduće projektovanje, proizvodnju, analizu i optimizaciju novih procesa koji uključuju faznu promenu materijala je razvoj visokoosetljivih kvantitativnih metoda zasnovanih na detekciji temperaturnih promena tokom trajanja procesa i korelaciji tih promena sa promenama u tretiranom materijalu. U ovom radu, sekundarna legura Al-8wt%Si-3wt%Cu je formirana iz tečnog stanja u uslovima slobodnog hlađenja. Identifikovane su karakteristične temperature transformacija i formalizovan je metod za praćenje količine čvrste faze tokom procesa očvršćavanja. Iz snimljene krive hlađenja određene su vrednosti prvog izvoda i formirana je odgovarajuća referentna kriva. Površina između prvog izvoda krive hlađenja i referentne krive je korišćena za praćenje količine očvrslog dela materijala tokom procesa očvršćavanja. Dobijeni rezultati su pokazali da je predložena metoda efikasna u dobijanju podataka o količini očvrslog dela materijala u svakom trenutku procesa očvršćavanja, kao i da se mogu dalje koristiti za detekciju broja faza i mikrokonstituenata u formiranoj strukturi i eksperimentalnu potvrdu latentne toplote očvršćavanja novih materijala. Metoda praćenja količine formirane čvrste faze u uslovima slobodnog hlađenja ne zahteva posebnu pripremu uzoraka niti kompleksnu laboratorijsku opremu, pa shodno tome, u praktičnoj primeni efikasno zamenjuje standardne metode za detekciju termofizičkih osobina materijala, kao što su diferencijalna termijska analiza ili diferencijalna skenirajuća kalorimetrija.One of the most effective ways for the future design, production, analysis and optimization of new processes, involving phase change of materials, is the development of highly sensitive quantitative methods based on the detection of temperature changes during the solidification process and the correlation of these changes with changes in the treated material. In this work, the secondary Al-8wt%Si3wt%Cu alloy was formed from the liquid state under free cooling conditions. Characteristic transformation temperatures were identified and a method for monitoring the amount of solid phase during the solidification process was formalized. From the recorded cooling curve, the values of the first derivative were determined and the corresponding reference curve was formed. The area between the first derivative of the cooling curve and the reference curve was used to assess the amount of solidified part of the material during the solidification process. The obtained results showed that the proposed method is effective in obtaining data of the fraction solid at every moment of the solidifcation process, as well as that it can be further used to detect the number of phases and microconstituents in the formed structure, as well as an experimental examination of the latent heat of solidification of new materials. The method of monitoring the amount of solid phase, formed under free cooling conditions, does not require specific preparation of samples or complex laboratory equipment, and accordingly, in practical application it effectively replaces standard methods for detecting thermophysical properties of materials, such as differential thermal analysis or differential scanning calorimetry

Kinetic of the ZnTiO3 to Zn2TiO4 phase transition observed on nano dimensional powder and polycrystalline bulk specimen using thermal analysis - DTA and dilatometer

Phase transition from ZnTiO3 to Zn2TiO4 represents second order phase transition from perovskite (zinc metatitanate) with a hexagonal ilmenite structure (R¯3) to inverse spinel (zinc orthotitanate) cubic structure (Fd¯3m) stable from room temperature to its melting (liquid) was identified during sintering of ZnTiO3 nanopowder. Kinetic of the phase transition has been observed as dimensional changes using dilatometric device thermo-mechanical analyzer TMA SETARAM model SETSYS Evolution and as thermal changes with SETARAM SETSYS Evolution TGA-DTA/DSC device. Two forms of specimens were employed nanopowder and polycrystalline sintered bulk specimen. It was found that sintering process and relaxation of the nanodimensional powder particles stress phenomena strongly influence kinetic of the phase transition. Dilatometric results known from previous investigations are now compared with differential thermal analysis results

Photovoltaics advancements for transition from renewable to clean energy

Moving from fossil fuels toward renewable resources of energy has a worldwide consensus. Solar energy alone can satisfy all our energy requirements since the earth receives 725 ZJ of energy from the sun each year while total human energy consumption in 2019 was 0.584 ZJ. The 2010s are highlighted as a transitional decade when the photovoltaic conversion industry transformed from a subsidized to a profitable energy sector. While photovoltaic energy conversion is a clean process, technologies for producing photovoltaic materials and solar panels affect the environment. The utilization of photovoltaic materials with low impact on the environment during the entire life cycle will mark the beginning of the sustainable transition toward 100% clean renewable energy sources in a sustainable manner. Thus far, only perovskite compounds have the potential to satisfy these requirements because of their theoretical conversion efficiencies, ease of synthesis, production scalability, adaptability, and comparability to existing photovoltaic systems. In this article, the rise of the photovoltaic industry in the last decade is shown and requirements in further transition from renewable to clean sources of renewable energy are foreseen.This is the peer-reviewed version of the article: Mitrašinović, A.M., 2021. Photovoltaics advancements for transition from renewable to clean energy. Energy 121510. [https://doi.org/10.1016/j.energy.2021.121510]Published manuscript: [https://hdl.handle.net/21.15107/rcub_dais_11796

Thermodynamic and kinetics investigation of elemental evaporation from molten Al7Si4Cu alloy

Treatment of liquid aluminum alloys in low vacuum conditions is often applied for parts production in the automotive and aerospace industry because of its effectiveness in removing dissolved gases. Because of the low vapour pressure of aluminum, concentrations of the most unwanted elements can be significantly reduced at lower pressures. Presented work analyzing kinetics parameters for elemental evaporation from liquid Al7Si4Cu alloy. The pressure inside mullite refractory material was below 2.1 kPa for melt temperatures between 760 and 910 °C. The alloy’s chemical composition was characterized by the Inductively Coupled Plasma Mass Spectrometry method. Lead, Zinc, and Mercury were reduced at the highest rate while the lowest evaporation occurred for key alloying elements such as Silicon and Copper. Higher evaporation rates were achieved at higher temperatures. The evaporation ratios, volatility coefficients, reaction rate constants, mass transfer coefficients, and elemental evaporation susceptibility on temperature increase were deduced for 16 elements. The obtained results confirmed that keeping molten aluminum alloys in low vacuum conditions for one hour is an efficient method in removing unwanted elements with great potential for further improvement in industrial conditions.Peer-reviewed manuscript: [https://hdl.handle.net/21.15107/rcub_dais_10002