Surface Topography Effects on the Fatigue Strength of Cast Aluminum Alloy AlSi8Cu3

Abstract

This article investigates the effect of the cast surface topography on the fatigue strength of the cast aluminum alloy AlSi8Cu3, which is equivalent to EN AC-46200 and A380 according to ASTM. Fatigue tests utilizing small-scale specimens under bending at a load stress ratio of R = 0 reveal a significant influence of the cast surface layer, leading to a reduction of the nominal fatigue strength at ten million load cycles by about one half. Fracture surface analysis highlights that crack initiation occurs because of both surface roughness and micropores within the cast surface layer. A numerical simulation procedure to assess the influence of the surface roughness on the fatigue strength is presented. Thereby, a three-dimensional mesh of an optically scanned surface topography is set up and a local fatigue strength reduction factor is numerically computed based on the critical distance approach by Taylor. The results reveal that the presented method slightly overestimates the fatigue strength compared to the experiments; however, the determined values lead to a sound accordance if the scatter of the fatigue test data points is considered.

Probabilistic Surface Layer Fatigue Strength Assessment of EN AC-46200 Sand Castings

“…It emerged that the trend of degree of porosity, as depicted in Figure 6, is representative for the T6 P1 specimens series. An increased degree of porosity near the cast surface of AlSi castings was also stated by Leitner et al [60]. This increased porosity formation may be reasoned by the oxide entrainment mechanism as a result of turbulent mould filling, see [61][62][63].…”

“…This increased porosity formation may be reasoned by the oxide entrainment mechanism as a result of turbulent mould filling, see [61][62][63]. However, a comprehensive insight in the degree of porosity can be more properly evaluated by means of XCT-scans [21,60].…”

A Probabilistic Fatigue Strength Assessment in AlSi-Cast Material by a Layer-Based Approach

“…In order to calculate the long-life fatigue strength σ LLF,j (SDAS, GEV α ) following Equation (12) for each HSV, material input parameters are required as follows. The base material strength σ LLF,0 was determined at specimens with HIP treatment; see the summary in Table 5.…”

“…As mentioned in [9], the shape of shrinkage-porosity, or microporosity, adopts the negative shape of the solidified dendrites, which can be subdivided into cavities and sponge shrinkage according to [10]. Another important impact factor regarding fatigue is the surface roughness, i.e., cast surface layer, analysed in more detail in [11][12][13], because surfaces often cannot be machined due to restrictions of accessibility within complex cast components. Surface texture can be assessed non-destructively by line-based [14,15] or area-based methodologies [13,16].…”