A new simple approach was developed to assess the Complete Melt Quality of aluminium cast alloys throughout the production line. The approach relies on the concurrent use of reduced pressure tests (RPT) and tensile tests at each station in the production line when the melt is transferred and/or processed. These tests can be used to determine the source of melt-related problems in the production line. Two case studies from the procedure of both an aluminium die-casting and a rheo-casting plant showed that melts were significantly damaged in the tower furnace and got progressively more damaged through the production line proven by the RPT, tensile test, and fracture surface analysis results.

The effectiveness of rotary degassing on the defect formation and mechanical properties of the final casting of aluminium alloy EN AC 46000 was investigated, along with its impact on the energy consumption in the casting furnace. In the melt preparation prior to casting, the molten metal is usually transported from the melting furnace to the casting furnace with rotary degassing as a cleaning procedure. Under the conditions of this specific study, negligible degradation was observed in the mechanical properties of the final cast component in an aluminium EN AC 46000 alloy after removing the rotary degassing step in the process. Furthermore, removing the rotary degassing step led to a reduced temperature drop in the melt, thus minimizing the need for reheating (energy consumption) by up to 75% in the casting furnace. The reduced energy consumption was up to 124,000 kWh in yearly production in a 1500 kg casting furnace. The environmental impact showed a similar to 1500 kg reduction in CO2 for one 1500 kg electrical casting furnace in a year.

The effect of copper (Cu) addition up to 3.2 wt% on crack initiation and propagation in an Al–Si–Mg cast alloy was investigated using in-situ cyclic testing in the as-cast condition. A combination of digital image correlation, electron backscatter diffraction, and scanning electron microscopy was used to investigate crack initiation and propagation behaviour during in-situ cyclic testing. The results showed that Cu-rich intermetallic compounds with the addition of Cu up to 1.5 wt% do not affect the fatigue behaviour of these alloys, and that crack propagation in these cases is trans-granular and trans-dendritic. However, increasing the concentration of the Cu retained in the primary α-Al matrix in solid solution and Cu-containing precipitates delayed crack propagation during cyclic testing. The results showed that strain accumulation was highest at the grain boundaries; however, the crack preferred to propagate along or across primary α-Al dendrites due to the relatively lower mechanical strength of the matrix compared to the eutectic and intermetallic phases. Moreover, the addition of Cu of more than 3.0 wt% to Al-Si-Mg alloys changes the fatigue behaviour that a rapid failure occurs. 

The study aimed to investigate crack initiation and propagation at the micro-scale in heat-treated Al–7Si–Mg cast alloys with different copper (Cu) contents. In-situ cyclic testing in a scanning electron microscope coupled with electron back-scattered diffraction and digital image correlation was used to evaluate the complex interaction between the crack path and the microstructural features. The three-nearest-neighbour distance of secondary particles was a new tool to describe the crack propagation in the alloys. The amount of Cu retained in the α-Al matrix after heat treatment increased with the Cu content in the alloy and enhanced the strength with a slight decrease in elongation. During cyclic testing, the two-dimensional (2D) crack path appeared with a mixed propagation, both trans- and inter-granular, regardless of the Cu content of the alloy. On fracture surfaces, multiple crack initiation points were detected along the thickness of the samples. The debonding of silicon (Si) particles took place during crack propagation in the Cu-free alloy, while cracking of Si particles and intermetallic phases occurred in the alloy with 3.2 wt% Cu. Three-dimensional tomography using focused ion beam revealed that the improved strength of the α-Al matrix changes the number of cracked particles ahead of the propagating crack with Cu concentration above 1.5 wt%.

Pores have been the main focus of quality assurance in castings. Latest research has shown that in aluminium castings pores can form only if there is existing entrainment damage, i.e., pores are merely the visible parts of the entrainment damage, and usually invisible damage is much more extensive. However, its effect on deformation behaviour has not been previously established or observed in-situ. This work applies 2D Digital Image Correlation (DIC) to an in-situ full-field stress-strain analysis of tensile samples with a non-conventional heterogeneous stress distribution. The observations reveal that the effect of hidden damage extends far beyond its impact on fracture behaviour and is responsible for initiating local strain concentrations during deformation. By extracting local stress-strain data, FE simulations have been performed to mimic the effect of local hidden damage on the heterogeneous stress-strain field. SEM and FIB-SEM analysis has been applied to investigate the cause for the strain concentrations. The combined results show that hidden damage in the form of oxide films is not only responsible for premature fracture, but also affects the deformation behaviour of tensile samples by introducing dispersed strain concentrations.

During in situ cyclic testing of hot isostatically pressed and heat-treated Al-5Si-0.5 Mg-1Cu alloy castings, cracks were observed to open up in places far away from the area of stress concentration. Cyclic testing was interrupted to assess these cracks. Analysis showed that these cracks originated from oxide bifilms that were entrained in the liquid state. Moreover, Si and Fe-rich intermetallics were observed to have precipitated on these bifilms. These finding makes it necessary to re-evaluate how damage is interpreted in mechanical studies. Entrainment damage, which takes place in the liquid state, may remain invisible in non-destructive inspection and can significantly affect fatigue properties when bifilms open up under low tensile stresses and present the propagating crack a path of low resistance during propagation.

This study has aimed to determine the effects of surface quality and pore size, obtained by different levels of hydrogen content of the liquid metal, on the fatigue behavior of an Al–7%Si–3%Cu–Mg casting alloy. Three surface conditions have been studied: as-cast rough, as-cast smooth, and standard machined and polished surface. The S–N curves have shown that surface roughness and hydrogen content individually impact fatigue strength. Surprisingly, the fatigue strength of machined and polished samples, which aligns with standard testing practices, is significantly reduced, compared to other conditions. Fatigue cracks have been observed to initiate at the pores just below the as-cast surface or on the machined surfaces. In all cases, pores have been observed to be surrounded by bifilms. Moreover, hydrogen content and roughness of the as-cast surface have been found to interact to determine the fatigue performance. These findings necessitate a re-evaluation of fatigue testing procedures for cast aluminum components.