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Purpose The purpose of this paper is to evaluate the effect of post process combinations, e.g. hot isostatic pressing (HIP) only, HIP + T6 heat treatments, and T6 only, with different aging time, on surface properties, microstructure and mechanical properties of stress-relieved AlSi10Mg parts produced by direct laser metal sintering. Design/methodology/approach HIP process and HIP + T6 heat treatments were applied to as stress-relieved direct laser metal sintered (DMLS) AlSi10Mg parts. Aging times of 4 and 12 h are selected to examine the optimum duration. To analyze the advantages of HIP process, a T6 heat treatment with 4 h of aging was also applied. Densities, open porosities and roughness values of as stress-relieved, HIPed, HIP + T6, and T6-only samples were measured. The samples were characterized by OM and SEM together with EDX analysis. An image analysis study was made to evaluate the inner pore structure, thereby to understand the mechanical behavior. Findings HIP process does not cause a significant change in surface porosity; yet it has a positive influence on inner porosity. HIP process results in a microstructure of the aluminum matrix surrounded by a network of micron and nano size Si particles. Additional heat treatment results in larger particles and precipitation. After HIPing, ductility increases but strength decreases. Samples aged 4 h present improved yield and tensile strength but decreased elongation, yet samples aged for 12 h reach a combination of optimum strength and ductility. The lower level of tensile strength and ductility in T6-only condition indicates that HIP process plays a crucial role in elimination of the porosity thus improves the effectiveness of subsequent heat treatment. Originality/value The study investigates the effect of post-process conditions and optimizes the aging time of the T6 heat treatment after HIP process in order to obtain improved mechanical properties. The stress-relieved state was chosen as the reference to prevent distortion during HIPing or heat treatment.

In this work, PM 316L based composite materials reinforced with SiC and emery powders in amounts of 5, 10 and 15 vol.-% were produced. The mixed powders were compacted by uniaxial pressing at 700 MPa and processed at 1160 and 1250uC for 1 h by means of conventional sintering and microwave sintering. The sintering atmospheres were Ar/H 2 95/5% for conventional sintering and Ar/H 2 90/10% for microwave sintering. Mechanical properties were evaluated with transverse rupture strength (TRS) tests. Densities and porosities were determined using Archimedes method. Sintered samples were characterised by optical microscopy and SEM. All of the composite materials had lower TRS values compared with 316L base material. Among all compositions, 5 vol.-% emery powder reinforced 316L alloy composite samples exhibited the most favourable mechanical and physical properties. The 10 vol.-%SiC containing composite samples also had acceptable properties. Moreover, microwave sintering yields better mechanical and physical properties.

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