Fatigue Crack Initiation on Semi-Solid Al–7Si–Mg Castings

Abstract

Four-point bending fatigue tests were performed on semi-solid Al–7Si–Mg castings with varying magnesium contents and heat treatment conditions. Additionally, the effect of anodising on the fatigue resistance of semi-solid Al–7Si–Mg castings was evaluated. Fracture surface and microstructure analysis showed that fatigue crack initiation occurred mainly at the periphery of regions of positive macrosegregation at the casting surface, resulting most likely from exudation. The microstructure of these macrosegregation regions was mostly eutectic and was frequently found surrounded by a layer of oxides. This layer of oxides promoted weak bonding between the macrosegregation region and the surrounding material and acted as a crack initiation site. In this study, primary α-Al globule agglomerates at the casting surface and surrounded by a layer of oxides also promoted fatigue crack initiation. Fatigue resistance of semi-solid Al–7Si–Mg castings in the T5 and T6 conditions increased with the increase in the magnesium content of the alloy from 0.3 to 0.45 wt.% due to the higher precipitation hardening response. However, the increase in the magnesium content from 0.45 to 0.6 wt.% resulted in a slight decrease in the fatigue resistance. The oxide layer formed during anodising had no significant effect on the fatigue resistance of the semi-solid Al–7Si–Mg castings in this study due to the dominant effect of the macrosegregation regions on fatigue crack initiation.

Integrity Assessment of Electron‐Beam‐Welded Joints of Additively Manufactured AlSi10Mg Components

“…The initiation of fatigue cracks in the vicinity of cavities already was numerously reported in the literature. [46][47][48] Comparing the results elaborated in the present study with the previous investigations [6,8] of some of the present authors on the FSW of AM aluminum alloys, it can be concluded that the higher cooling rate in EBW rather than FSW can cause the formation of fine and dispersed Si-rich particles and, hence, higher hardness and strength in the WZ. Although FSW is capable of considerable grain refinement, the size and morphology of Si-rich particles seem to govern the strength of AlSi10Mg alloy.…”

“…The initiation of fatigue cracks in the vicinity of cavities already was numerously reported in the literature. [ 46–48 ]…”

Influence of Applied Load and Sliding Distance on Wear Performance of AlSi7Mg0.6 Aluminum Alloy

“…The substrate of positioning supports is a cast aluminum alloy, AlSi7Mg0.6 (A357). Most previous studies focus on the tensile [8][9][10][11] and fatigue properties [12][13][14][15] of AlSi7Mg0.6. Hirsch et al [8] indicated that the surface hardness and yield strength of A357 increased by 100% and 80%, respectively, for the materials With unique combinations such as high strength-to-weight ratio, excellent castability, supreme corrosion resistance and benign wear behavior, aluminum alloys are utilized in many scenarios.…”

“…Investigations by Serrano-Munoz et al [13] and Dezecot et al [14] indicated that fatigue failures generally originate from the casting defects of the cast A357 aluminum alloy. Santos et al [15] performed four-point bending fatigue tests on semi-solid Al-7Si-Mg castings with varying magnesium contents and eval-uated the effect of anodizing on the fatigue resistance. In the case of positioning supports, fatigue failures rarely appear, while wear failures occur frequently.…”