Selective Laser Melted AlSi10Mg Alloy Research Articles

Effects of hot isostatic pressing and internal porosity on the performance of selective laser melted AlSi10Mg alloys

We herein report the preparation of AlSi10Mg alloys with a range of porosities by selective laser melting (SLM) and subsequent hot isostatic pressing (HIP). The microstructures and mechanical properties of the resulting alloys were then investigated, and the influence of the internal porosity on the mechanical properties was investigated. Under the optimum laser irradiation conditions, the tensile strength of the alloy was very high; however, this tensile strength decreased with increasing the internal porosity. Following HIP, both the proof and tensile strengths decreased significantly due to drastic changes in the microstructures, i.e., the fine dendritic cell microstructure changed to granular precipitated Si phases. In addition, the initial porosity had a relatively small effect on the proof and tensile strengths and these strengths were comparable for all materials. In contrast, the ductility of the alloy improved significantly after HIP; however, it deteriorated as the initial porosity was increased. This was accounted for by the fact that HIP treatment was not really effective for eliminating the internal pores in the SLM AlSi10Mg alloy. Therefore, the reduction of internal pores by the optimization of laser irradiation conditions is essential in the fabrication of SLM aluminum alloys.

Study on magnetic abrasive finishing of AlSi10Mg alloy prepared by selective laser melting

Selective laser melting (SLM) technology is playing an increasingly important role in today’s manufacturing industry. However, the surface quality of SLM samples is relatively poor and cannot be directly applied to industrial production. Therefore, this paper focuses on the post-treatment process of SLM AlSi10Mg alloy. First, the rough machining is performed by a grinding process (GP), and then, the magnetic abrasive finishing (MAF) is used for finish machining. The experiment results show that the combination of GP and MAF can effectively reduce the surface roughness and improve the surface quality of SLM AlSi10Mg alloy. The GP reduced the surface roughness to drop from 7 μm (after SLM forming) to about 0.6 μm, and the rough surface with defects such as spheroids and pits evolved into the fine surface with scratches and pores. The MAF reduced the surface roughness to a minimum of 0.155 μm, which resulted in excellent surface morphology. The surface hardness after the GP was higher, and the MAF reduced the hardness of the GP surface.

Influence of the annealing and defects on the VHCF behavior of an SLM AlSi10Mg alloy

AbstractIn the paper, the influence of the annealing temperature on the Very High Cycle Fatigue (VHCF) of AlSi10Mg specimens produced through selective laser melting (SLM) is experimentally assessed. VHCF tests at 20 kHz are carried out on Gaussian specimens subjected to a heat treatment suggested by the system supplier (heating for 2 hours to 320°C and air cooling) and to a heat treatment proposed by the authors (heating for 2 hours to 244°C and air cooling). The defects originating failure and the conditional P‐S‐N curves are compared. Experimental results show that an annealing temperature of 320 ° C induces the spheroidization of the Si network, which enhances the ductility but has a negative effect on the VHCF response. On the contrary, by reducing the heating temperature to 244 ° C, the original as‐built microstructure is not altered and the minimization of the residual stresses permits to enhance the VHCF response.

Abnormal corrosion behavior of selective laser melted AlSi10Mg alloy induced by heat treatment at 300 °C

Heat treatment is often employed to control the mechanical properties of selective laser melted (SLMed) AlSi10Mg, which also alters its microstructure and corrosion resistance. Therefore, a SLMed AlSi10Mg alloy was heat treated at 300 °C and 400 °C for 2 h to investigate its microstructural evolution and corrosion behavior. Abnormal corrosion behavior is observed in the sample heat treated at 300 °C. Heat treatment destroys the cellular Si network in the microstructure of the SLMed AlSi10Mg sample and promotes the formation of extremely fine Si particles; in contrast, such a microstructure cannot form a protective film on the surface of the sample, which leads to rapid corrosion along the cracked Si network inward to the inner Al matrix without the microgalvanic effect.

Influence of static magnetic field on microstructure and mechanical behavior of selective laser melted AlSi10Mg alloy

In this work, the influence of a static magnetic field on the microstructure and mechanical behavior of AlSi10Mg alloy was studied. Our findings show that the applied magnetic field results in increase of the relative density and decrease of cellular dendrite spacing in the processed material. Moreover, the fraction of grains with a columnar morphology decreases and the fraction of equiaxed grains increases with increasing magnetic field intensity. As a result, the AlSi10Mg alloys fabricated via selective laser melted (SLM) with a superimposed magnetic field exhibited both a high ultimate tensile strength and ductility, which are superior to the AlSi10Mg alloys using identical process parameters without magnetic field. Furthermore, the influence of a static magnetic field on the melt pool scale and mushy zone scale was analyzed and simulated numerically. Our results suggest that the decrease pores density may be attributed to magnetic damping of convection and the volume force imposed on the cellular dendrite reaches 105 N/m3, which is sufficient to fracture the columnar grains and refine the cellular dendrite spacing. The present study provides novel insight into the potential of using a superimposed magnetic field during SLM processing and the associated benefits in terms of materials performance.

CNT-reinforced AlSi10Mg composite by selective laser melting: microstructural and mechanical properties

ABSTRACTCarbon nanotube (CNT)-AlSi10Mg composites were fabricated by selective laser melting (SLM). The influence of CNTs on the density, microstructure, and strength of SLM CNT-AlSi10Mg composites was investigated. The addition of CNTs over 0.1 wt-% significantly damaged the density due to the high surface energy of the CNTs. The network Si eutectic had no significant difference in either the SLM AlSi10Mg alloy or the CNT-AlSi10Mg composite. Reserved CNTs with a short scale were observed in the SLM CNT(0.5 wt-%)-AlSi10Mg composite. The ultimate tensile strength of the 0.05 wt-% CNT-AlSi10Mg composite was 441.2 ± 0.9 MPa, which was higher than that of AlSi10Mg alloy. The grain boundary strengthening played an important role in the reinforcement of CNT-AlSi10Mg composite because of the refined grain.

Corrosion Behavior of Selective Laser Melted AlSi10Mg Alloy in NaCl Solution and Its Dependence on Heat Treatment

This work investigates the corrosion behavior of AlSi10Mg alloy produced by selective laser melting (SLM) and the counterparts heat-treated at 450–550 °C in 3.5 wt% NaCl solution. Electrochemical measurements and weight loss tests together with microstructural characterizations were conducted. The SLM-produced alloy displays a microstructure with a continuous network of Si particles, exhibiting superior corrosion behavior. After heat treatment, the Si particles are coarsened and isolated and Al matrix dissolves into their surrounding area, thereby degrading the corrosion resistance properties. Therefore, the corrosion resistance of AlSi10Mg alloy degrades with increasing the heat treatment temperature.

Influence of Selective Laser Melting Machine Source on the Dynamic Properties of AlSi10Mg Alloy.

Selective laser melting (SLM) AlSi10Mg alloy has been thoroughly investigated in terms of its microstructure and quasi-static properties, owing to its broad industrial applications. However, the effects of the SLM process on the dynamic behavior under impact conditions remain to be established. This research deals with the influences of manufacturing process parameters on the dynamic response of the SLM on AlSi10Mg at a high strain rate of 700 to 6700 s−1 by using a split Hopkinson pressure bar apparatus. Examinations were performed on vertically and horizontally built samples, processed individually by two manufacturers using a different laser scanning technique on the same powder composition. It was concluded that the fabrication technique does not influence the true stress–true strain dependency at strain rates of 700 to 2800 s−1. However, at higher strain rates (4000 to 6700 s−1), this study revealed different plastic behavior, which was associated only with the horizontally built samples. Moreover, this study found different failure demeanors at true strains exceeding 0.8. The dynamic response was correlated with the as-built microstructure and crystallographic texture, characterized using the electron backscattered diffraction technique.

Very high-cycle fatigue properties and microstructural damage mechanisms of selective laser melted AlSi10Mg alloy

The influence of cooling rates in selective laser melted AlSi10Mg on fatigue properties is studied. The failure mechanisms during quasistatic and fatigue loading were analyzed using electron microscopy, X-ray computed tomography and ultrasonic fatigue testing systems. It was found that even when densification mechanism was not significantly enhanced, the morphology of defects was adopting more regularly spherical shape which is less critical under structural loading. The controlled cooling introduced microstructural homogeneity and further property enhancement of the microstructure which contributed to higher quasistatic and fatigue strength in this study and compared to the literature on the same alloy. Elimination of semi-coherent Si agglomerates on the melt pool boundaries impeded crack propagation and forced it to adjust to a perpendicular orientation to the columnar dendrites formed instead. The strengthening mechanism was shown effective in quasistatic, servohydraulic and ultrasonic fatigue tests in very high-cycle fatigue. The influence of testing at ultrasonic frequencies was analyzed through the fatigue data and influence was not significant. Analysis of the interrupted fatigue specimens in the X-ray computed tomography revealed a pore-crack interaction mechanism which was hypothesized earlier in the literature. Although impedance of crack propagation and theoretical drop of stress intensity factors at crack tips was expected, it was implied that recommence of crack propagation and the end life of the specimen will still be dependent on the local strength of the microstructure in the vicinity of the pore.

Microstructure of selective laser melted AlSi10Mg alloy

The influence of laser power during selective laser melting (SLM) on the grain morphology and texture component in AlSi10Mg alloy has been investigated, using electron backscattered diffraction (EBSD). Both equiaxed and columnar grains were observed. The formation of equiaxed grains was attributed to the huge thermal gradient on the border of melt pool and the columnar to equiaxed transition (CET) occurred in front of the columnar grains. The grain size of low laser power sample was found smaller than that of higher ones. A fine pseudoeutectic structure, in which Si existed as fibrous, was observed because of the high cooling rate. This paper, from a new angle, explained the formations of three different zones across the melt pool, which were differentiated by the morphology of Si phase. The three zones correspond to the three temperature zones, which were divided by liquidus and solidus temperature, during the heating by laser beam. The coarse zones are formed by reheating the basic metal to semi-solid state when the temperature is lower than the liquidus temperature but higher than the solidus temperature.

Influence of working environment and built orientation on the tensile properties of selective laser melted AlSi10Mg alloy

AlSi10Mg alloy was fabricated by Selective Laser Melting (SLM) using two different atmospheres, argon and nitrogen, both in vertical and horizontal built directions. The influence of work environment and anisotropy are studied in this work by keeping all other process parameters including shielding gas pressure constant. The meso-structural features revealed scan tracks and melt pool layers while the microstructural features have showed cellular structure with α-Al matrix and its boundary made up of the eutectic mixture of Al and Si. These cells were approximately of 500 nm size as revealed by TEM analysis. The grain morphology and texture were studied using EBSD analysis. The XRD analysis revealed similarity in the phases formed in samples built under argon and nitrogen environment. Both the horizontal as well as vertical built samples contain elongated grains with 〈100〉 direction oriented along the built direction and 〈100〉 fibre texture in the XY plane. Tensile test results showed the maximum strength of 385 ± 5 MPa was exhibited by vertically built sample under nitrogen environment while the lowest strength of 338 ± 2 MPa was exhibited by horizontally built sample under argon environment. Surface roughness and porosity measured in all the conditions exhibited minor variation in the average surface roughness and porosity area fraction values. Among the samples tested under same built orientation, the variation in strength is approximately 5% higher in nitrogen environment while among the samples tested under same working environment, the variation in strength is approximately 7.5% higher in vertically built samples. This states that the influence of working environment on strength is lesser than that of the built orientation. The materials exhibited brittle failure with inclined fracture profile, fracture morphology with pores, river patterns and inter-cellular fracture plus approximately 4.5% elongation in all the tested samples, implied isotropic elongation behaviour. The samples built under both the work environments exhibited the similarity in defect structure, microstructure and nearly isotropic behaviour in mechanical properties. It inferred that nitrogen could be preferred over argon as shielding gas in SLM for its cost effectiveness.

Dynamic Versus Quasi Static Fracture Toughness of Additively Manufactured AlSi10Mg Alloy by Selective Laser Melting Technique

In today's additive manufacturing sector, one of the most popular areas is selective laser melting (SLM) due to its capability of producing geometrically complex metal parts directly from CAD model in a few short steps. Many studies have been reported on static mechanical properties of SLM components; however, dynamic properties of SLM components of different materials have not been thoroughly investigated. Only few papers have been published on the dynamic mechanical behavior, especially in the crack resistance of selective laser melted AlSi10Mg alloy. In the present study, the effect of loading rate, dynamic versus quasi static, on the fracture toughness of the as-built alloy (X and Z orientations) has been investigated. The experimental results revealed the inherently anisotropic behavior for loading rates where the Z orientation exhibited lower toughness compared to the x orientation. The dynamic loading by impact, resulted in a significant decrease of the toughness values up to about 50% compared to the quasi-static loading. This mechanical response was attributed to the increase in the yield stress which alters the state stress at the crack tip from the planestress to some extent of the mix-mode plane stress/strain.

Role of melt pool boundary condition in determining the mechanical properties of selective laser melting AlSi10Mg alloy

We describe here a comprehensive study on the effect of cellular structure and melt pool boundary (MPB) condition on the mechanical properties, deformation and failure behavior of AlSi10Mg alloy processed by selective laser melting (SLM). The morphology of melt pool (MP) on the load bearing face of tensile samples was significantly different with build directions. It resulted in different mechanical properties of the samples with different build directions. Furthermore, the microstructure analysis revealed that the MP in the SLM AlSi10Mg alloy mainly consisted of columnar α-Al grains which were made of ultra-fine elongated cellular structure. Electron back-scatter diffraction (EBSD) analysis revealed that the long axis of cellular structure and columnar grains were parallel to < 100 >, which resulted in < 100 > fiber texture in SLM AlSi10Mg alloy. However, Schmid factor calculation demonstrated that the anisotropy of mechanical properties of the SLM AlSi10Mg alloy built with different direction was mainly dependent on the distribution of MPB on the load bearing face, and not texture. The defects including pores, residual stress and heat affected zone (HAZ) located at MPB made it the weakest part in the SLM AlSi10Mg. The sample built along horizontal direction exhibited good combination of strength and plasticity and is attributed to the lowest fraction of MPBs that withstand load during tensile. MPB had strong influence on the mechanical properties and failure behavior of SLM AlSi10Mg built with different directions.

Effect of post-process heat treatment on microstructure and properties of selective laser melted AlSi10Mg alloy

In the present work, the model alloy of AlSi10Mg was prepared by selective laser melting, and further annealed by two kinds of heat treatment regimes, i.e. A1 (300 °C/2h+ water quench) and A2 (535 °C/1h+ water quench + 190 °C/10 h+ furnace quench). The samples were investigated by XRD, SEM, EBSD, room temperature tensile and nanoindentation tests, to understand the effect of heat treatments on the phase constituents, microstructure, residual stress and mechanical properties of the laser additive manufactured AlSi10Mg alloy. The experimental results showed that, the heat treatment method of A1 is an effective heat treatment regime for eliminating the residual stress and improving the comprehensive mechanical properties for structural applications.

Strength and strain hardening of a selective laser melted AlSi10Mg alloy

In this paper, we report that a selective laser melted (SLM) AlSi10Mg alloy has unique hierarchical microstructures. There are micro-sized Al grains and transgranular ultrafine cellular structures around primary Al, and the cell boundary is made up of alternate eutectic Si and eutectic Al phases. The SLM AlSi10Mg alloy has both high tensile strength and high strain-hardening capability, which are superior to Al-Si alloys fabricated by conventional powder metallurgy and cast methods. Post-tensile high-resolution microscopy analyses provide further evidence supporting Orowan looping as a strengthening mechanism of the SLM Al-Si alloy.