To resolve the poor weldability of ductile irons, this study employed AISI 1008 low carbon steel in the pure ferrite phase as the top plate and ductile iron as the bottom plate and varied the rotational speeds combined with travelling speeds that ranged between 40 and 70 mm min 21 to conduct a friction stir lap welding test. After welding, the weldments underwent microstructure analysis and hardness testing followed by a tensile shear test to evaluate the joint strength. At low rotational speeds ,800 rev min 21 , the experimental results indicated the following: the interfacial regions of the two materials could not join completely; the matrix structure of the stir zone was primarily composed of pearlite; the original spherical shape of the graphite in the ductile iron matrix changed into a striped conformation; the weldments possessed low average maximum tensile load; and the fracture site was in the vicinity of the weld interface. At the transition parameter of 850 rev min 21 , the average maximum tensile load of weldment increased, and the tensile fracture site was in the interface of retreating site. The results under high rotational speeds of 900 and 1000 rev min 21 indicated the following: an excellent joining effect was achieved; the interfacial regions of the carbon steel and ductile iron primarily comprised pearlite, although the vicinity of the retreating side and the stir zone matrix of ductile irons were composed of martensite structures; individual graphite granules were present; the average maximum tensile load of the weldments was the highest; and the fracture site was located in the low carbon steel base metal.
In this study, AZ91 magnesium-alloy-based metal matrix composites (MMCs) reinforced with 10 wt% of Al0.5CoCrFeNi2 high-entropy alloy (HEA) particles and SiC particles were prepared by a spark plasma sintering (SPS) process at 300 °C. The effects of reinforcements on the microstructure and mechanical properties of AZ91-based MMCs were studied. The results showed that AZ91–HEA composite consisted of α-Mg, Mg17Al12 and FCC phases. No interfacial reaction layer was observed between HEA particles and the Mg matrix. After adding HEA into AZ91, the compressive yield strength (C.Y.S) of the AZ91–HEA composite increased by 17% without degradation of failure strain. In addition, the increment in C.Y.S brought by HEA was comparable to that contributed by commonly used SiC reinforcement (15%). A relatively low porosity in the composite and enhanced interfacial bonding between the α-Mg matrix and HEA particles make HEA a potential reinforcement material in MMCs.
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