Improving mechanical properties of Mn-added hypoeutectic Al-4Ni alloy by friction stir processing

The effects of Mn addition (1 wt.%, 2 wt.% and 4 wt.%) and friction stir processing (FSP) on the microstructure and mechanical properties of Al-4Ni alloy were studied. The results showed that Mn promoted the formation of Al6Mn and Al60Mn11Ni4 intermetallics. These Mn-rich compounds increased the strength and hardness, but decreased the ductility and fracture toughness of the alloy. To improve the ductility and toughness, the as-cast alloys were then subjected to FSP (rotation speed of 1600 r/min and traverse speed of 12 mm/min). According to the results, FSP greatly improved the mechanical properties. The tensile strength, yield strength, fracture strain, microhardness, and fracture toughness of FSPed Al-4Ni-2Mn increased by 67%, 30%, 230%, 20%, and 1185%, respectively. The fine redistribution of Mn-rich compounds, formation of ultrafine grains, microstructural densification, and the elimination of casting defects such as micropores and oxide bifilms were found to be the most important factors responsible for improving the mechanical properties. The fractographic investigations also revealed that the fracture of as-cast Mn-rich alloys changed from the brittle mode containing micro-facets to a more ductile fracture mode containing fine and equiaxed dimples in FSPed alloys.

Tensile properties and hot tearing susceptibility of cast Al–Cu alloys containing excess Fe and Si

This study was undertaken to investigate the tensile properties and hot tearing susceptibility of cast Al–Cu alloys containing excess Fe(up to 1.5 wt%)and Si(up to 2.5 wt%).According to the results,the optimum tensile properties and hot tearing resistance were achieved at Fe/Si mass ratio of 1,where theα-Fe phase was the dominant Fe compound.Increasing the Fe/Si mass ratio above unity increased the amounts of detrimentalβ-Cu Fe platelets in the microstructure,deteriorating the tensile properties and hot tearing resistance.Decreasing the mass ratio below unity increased the size and fraction of Si needles and micropores in the microstructure,also impairing the tensile properties and hot tearing resistance.The investigation of hot-torn surfaces revealed that theβ-Cu Fe platelets disrupted the tear healing phenomenon by blocking interdendritic feeding channels,while theα-Fe intermetallics improved the hot tearing resistivity due to their compact morphology and high melting point.

Improvement of Surface Mechanical and Tribological Characteristics of L-PBF Processed Commercially Pure Titanium through Ultrasonic Impact Treatment

Multi-pass ultrasonic impact treatment(UIT)was applied to modify the microstructure and improve the mechanical and tribological characteristics at the near-surface region of commercially pure Ti(CP-Ti)specimens produced by the laser powder bed fusion(L-PBF)method.UIT considerably refined the L-PBF process-related acicular martensites(α′-M)and produced a well-homogenized and dense surface microstructure,where the porosity content of 1-,3-,and 5-pass UITed samples was reduced by 43,60,and 67%,respectively.The UITed samples showed an enhancement in their near-surface mechanical properties up to a depth of about 300μm.The nanoindentation results for the 3-pass UITed sample revealed an increase of about 53,45,and 220%in its nanohardness,H/E_(r),and H_(3)/E_(r)^(2)indices,respectively.The stylus profilometry results showed that performing the UIT removed the L-PBF-related features/defects and offered a smooth surface.The roughness average(R_(a))and the skewness(R_(sk))of the 3-pass UITed sample were found to be lower than those of the L-PBFed sample by 95 and 223%,respectively.Applying the UIT also enhanced the material ratio,where the maximum load-bearing capacity(~100%)in as-L-PBFed(as-built)and 3-pass UITed samples was obtained at 60-and 10-µm depths,respectively.The tribological investigations showed that applying the UIT resulted in a significant reduction of wear rate and average coefficient of friction(COF)of CP-Ti.For instance,under the normal pressures of 0.05 and 0.2 MPa,the wear rate and COF of the 3-pass UITed sample were lower than those of the L-PBFed sample by 65 and 58%,and 20 and 17%,respectively.