Stefano Capuzzi

Optimization of a Permanent Step Mold Design for Mg Alloy Castings

The design of a permanent Step mold for the evaluation of the mechanical properties of light alloys has been reviewed. An optimized Step die with a different runner and gating systems is proposed to minimize the amount of casting defects. Numerical simulations have been performed to study the filling and solidification behavior of an AM60B alloy to predict the turbulence of the melt and the microshrinkage formation. The results reveal how a correct design of the trap in the runners prevents the backwave of molten metal, which could eventually reverse out and enter the die cavity. The tapered runner in the optimized die configuration gently leads the molten metal to the ingate, avoiding turbulence and producing a balanced die cavity filling. The connection between the runner system and the die cavity by means of a fan ingate produces a laminar filling in contrast with a finger-type ingate. Solidification defects such as shrinkage-induced microporosity, numerically predicted through a dimensionless version of the Niyama criterion, are considerably reduced in the optimized permanent Step mold.

Influence of Coating and De-Coating on the Coalescence of Aluminium Drops in Salt

In a rotary furnace for aluminium recycling and dross treatment, a salt flux is added which protects against oxidation and captures non-metallic impurities. Furthermore, the salt has to promote the coalescence of the metal drops in the dross. This work investigates the coalescence of molten aluminium for different types of scrap. One hundred discs were stamped from aluminium alloy sheets with and without coating. They were melted, covered in NaCl–KCl–Na3AlF6 molten salt, in an induction furnace at 790 °C. The solidified aluminum droplets were extracted by leaching the salt with water. The fraction of coalesced drops and the average diameter were determined to evaluate the coalescence efficiency. The effect of various de-coating temperatures was studied. The results show that the coalescence is negatively affected by coating. Long holding times has no effect. Complete coalescence off all discs are achieved with uncoated scrap. The drops coalesce if the temperature of the combustion reaction for the coating is attained.

Influence of Ageing Heat Treatment on Microstructure and Mechanical Properties of a Secondary Rheocast AlSi9Cu3(Fe) Alloy

The effects of different process parameters (temperature and time) during the ageing treatment on the microstructure and the mechanical properties of a secondary rheocast AlSi9Cu3(Fe) alloy have been examined. Optical microscope investigations have been performed to qualitatively study the microstructure of the as-rheocast and thermal treated alloys. Transmission electron microscopy technique and selected area electron diffraction analyses have been used to characterize the hardening phases precipitated in the Al-matrix during the different ageing stages. The evolution of mechanical properties of the Al matrix has been monitored by micro-hardness testing.

Study of fluxing in Al refining process by rotary and crucible furnaces

Abstract The process used to obtain recycled Al alloys depends on the scrap quality. Rotary furnaces are normally used in Europe as they allow a great productivity and they can process low quality scrap using a salt flux to protect the molten metal from oxidation. In this article, the effect of the quantity of salt on the metal recovery has been experimentally investigated by melting several types of scrap under a mixture of NaCl–KCl–Na3AlF6 salts. The quantity of salt has been related to the salt factor (SF), which is the ratio between the non-metallic content in the scrap and the quantity of salt required. The same levels of salt factor have been tested by melting the scrap in rotary and crucible furnaces. The metal recovery increases with the salt content for both furnaces. The results obtained with the different melting processes are comparable because the yield difference is similar considering different salt factors. Crucible furnace gives greater metal recovery but it cannot replace rotary furnace in Al refining industry due to lower melting capacity. However, the results highlight that the optimisation of the Al refining process can be supported by preliminary tests through crucible furnaces reducing the time and material consumptions.

Evolution of Primary Fe-Rich Compounds in Secondary Al-Si-Cu Alloys

Although iron is usually added in die cast Al-Si foundry alloys to prevent die soldering, primary Fe-rich particles are generally considered as “hardspot” inclusions which compromise the mechanical properties of the alloy, namely ductility and toughness. As there is no economical methods to remove the Fe excess in secondary Al-Si alloys at this time, the control of solidification process and chemical composition of the alloy is a common industrial practice to overcome the negative effects connected with the presence of Fe-rich particles. In this work, the size and morphology as well as the nucleation density of primary Fe-rich particles have been studied as function of cooling rate and alloy chemical composition for secondary Al-Si-Cu alloys. The solidification experiments were carried out using differential scanning calorimetry whereas morphology investigations were conducted using optical and scanning electron microscopy. Mcrosegregations and chemical composition of primary Fe-rich particles were examined by energy dispersive spectroscopy.

Investigation of Primary Fe-Bearing Compounds in Secondary Aluminium Alloys by Differential Scanning Calorimetry

The precipitation of primary Fe-rich intermetallics (sludge) in AlSi9Cu3(Fe) type alloys has been investigated for different Fe, Mn and Cr contents and cooling rates. Differential scanning calorimetry was used in order to assess the nucleation temperature and the enthalpy of sludge particles as well as to follow their evolution. The results show that the sludge nucleation temperature and the release of latent heat during sludge formation are functions of the initial concentrations of Fe, Mn and Cr in the molten alloy, i.e. the sludge factor, and the cooling rate. Being able to predict the temperature of sludge formation will support the foundries to set the right molten metal temperature in order to prevent sludge precipitation during the entire high-pressure die-casting process.

Microstructure and Mechanical Properties of Automotive Components Die Cast with Secondary Aluminum Alloys by Seed Semi‐Solid Process

The microstructure and mechanical properties of an automotive component die-cast by Swirled Enthalpy Equilibration Device process are analyzed. Two secondary aluminum alloys have been used, AlSi7Cu3Mg and AlSi9Cu3(Fe) alloys. The castings have been investigated by means of computer tomography to evaluate the concentration and distribution of casting defects, especially in the regions of thick wall thickness. Microstructural investigation has been carried out by means of optical microscope and image analysis technique. The results reveal a not uniform distribution of primary α-Al globules throughout the casting, with a solid fraction ranging from 48 to 58%, and eutectic segregation phenomena. The castings have been mapped in terms of mechanical properties and quality index. The variation of the mechanical properties reflects the presence of local casting defects and alloying segregation.