Commercial AlSi7Mg alloy represents the usual choice for complex geometry casting production. The market imperative to improve mechanical properties imposed the design of new chemical composition of AlSi7MgCu alloy with high content of Cu (up to 1.435 wt.%). This represents a challenge in order to achieve advanced properties. The interaction of a number of alloying (Si, Mg, Cu) and trace elements (Fe, Mn) influenced a wide range of complex reactions occurring and therefore leading to intermetallic phase precipitation. The characterization of novel chemical composition interaction and its solidification sequence was achieved by modelling an equilibrium phase diagram, simultaneously performing both thermal analysis and metallographic investigations. Copper influence was indicated in the whole solidification process starting with infiltration in modified Chinese script phase Al15(Fe,Mn,Cu)3Si2, beside common intermetallic Al5FeSi. Copper addition encourages formation of compact complex intermetallic phases Al5Cu2Mg8Si6 and Al8(Fe,Mn,Cu)Mg3Si6. Solidification ended with secondary eutectic αAl + Al2Cu + βSi. Microstructure investigation allows volume reconstruction of the microstructure and distribution of particular phases. Chemical compositions enriched in copper content and developed microstructural constituent through solidification sequence of AlSi7MgCu alloy contribute to a significant increase in mechanical properties already in an as-cast state.
Aluminum alloys are widely applied in automotive, aircraft, food, and building industries. Multicomponent technical AlSi9MgMn alloy is primarily intended for high cooling rate technology. Controlled addition of alloying elements such as iron and manganese as well as magnesium can improve mechanical and technological properties of the final casting depending on the cooling conditions during solidification. The aim of this investigation is the characterization of AlSi9MgMn alloy microstructure and mechanical properties at lower cooling rates than those for which this alloy was primarily developed. Thermodynamic calculation and thermal analyses revealed solidification sequence in correlation to the microstructure investigation as follows: development of primary dendrite network, precipitation of high temperature Al15(Mn,Fe)3Si2 and Al5FeSi phases, main eutectic reaction, precipitation of intermetallic Al8Mg3FeSi6 phase, and Mg2Si as a final solidifying phase. Influence of microstructure features investigation and cooling rate reveals significant Al15(Mn,Fe)3Si2 morphology change from Chinese script morphology at low, irregular broken Chinese script morphology at medium, and globular morphology at high cooling rate. High manganese content in AlSi9MgMn alloy together with high cooling rate enables the increase of Fe+Mn total amount in the intermetallic Al15(Mn,Fe)3Si2 phase and encourage favourable morphology development, all resulting in enhanced mechanical properties in as-cast state.
In this research, an often-used high-pressure die-casting (HPDC) AlSi9Cu3(Fe) alloy was chosen as the matrix for an Al-alloy/MWCNT nanocomposite material that could be, in the case of targeted mechanical properties, used for the production of lighter car parts. In the industrial experiment, nanocomposite samples were prepared by a HPDC machine from a base AlSi9Cu3(Fe) alloy with three different mass ratios of MWCNTs placed on two different positions inside the casting machine. The structure and thermal stability of the used MWCNTs were visually confirmed by scanning electron microscopy (SEM). The microstructural and metallographic properties were studied using an optical microscope. The mechanical properties (tensile strength, elongation at break and hardness) were investigated using a universal testing machine and a Vickers hardness tester. The experimental results of this research showed that the HPDC-prepared Al-alloy matrix nanocomposite material had significantly changed mechanical properties even with small MWCNT contents. The elongation at break and the tensile strength of the Al-alloy/MWCNT nanocomposite were increased in comparison with the base alloy. The finest microstructure was shown by samples with 0.05 w/% MWCNTs, which was in correlation with the most significant change in the mechanical properties. Keywords: metal-matrix nanocomposites, AlSi9Cu3(Fe) alloy, multi-walled carbon nanotubes (MWCNT), high-pressure die casting (HPDC) Avtorji opisujejo raziskavo izdelave nanokompozitnega materiala s kovinsko osnovo iz zlitine AlSi9Cu3(Fe). Za oja~itveno fazo so uporabili ve~stenske ogljikove nanocev~ice (MWCNT). Za izdelavo kompozita so uporabili visokotla~no brizganje taline v kovinsko orodje oz. deljivi model (HPDC). Ta postopek se najbolj pogosto uporablja za izdelavo lahkih avtomobilskih delov s specifi~nimi mehanskimi lastnostmi. Izvajali so industrijske preizkuse na HPDC stroju in pri tem uporabili kovinsko talino AlSi9Cu3(Fe) s tremi razli~nimi dodatki MWCNT, ki so jih postavili na dve razli~ni mesti v votlini orodja. Strukturno in termi~no stabilnost uporabljenih MWCNT so potrdili s preiskavo ulitkov pod vrsti~nim elektronskim mikroskopom (SEM). Nadalje so izvedli {e metalografske preiskave mikrostrukture pod opti~nim mikroskopom. Mehanske lastnosti izdelanih materialov, natezno trdnost in raztezek po prelomu, so dolo~ili na univerzalnem trgalnem stroju, medtem ko so trdoto dolo~ili na standardnem Vickersovem merilniku. Eksperimentalni rezultati te preiskave so pokazali, da so se mehanske lastnosti s postopkom HPDC izdelanega nanokompozita na osnovi Al zlitine znatno spremenile`e pri dodatku dokaj malih koli~in MWCNT. Natezna trdnost in raztezek po prelomu nanokompozita MWCNT/Al-zlitina sta v primerjavi z osnovno Al zlitino narasla. Najbolj drobnozrnato mikrostrukturo so imeli vzorci z dodatkom 0,05 masnih dele`ev MWCNT, kar se je ujemalo z najve~jo spremembo mehanskih lastnosti. Klju~ne besede: nanokompoziti s kovinsko osnovo, zlitina AlSi9Cu3(Fe), ve~stenske ogljikove nanocev~ice (MWCNT), visok...
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