Effect of temperature on silicon particle damage in A356 alloy

Abstract

fringes due to double diffraction from (1-101) M2C reflections is presumably due to their relatively higher intensities resulting in intense double diffraction spots.An examination of the results of the present and previous studies on the secondary hardening high performance steels indicates the following.(1) The black-white strain contrast indicating coherency of the carbides with the ferrite matrix was observed only until the peak aging temperature of 482 ЊC.(2) The appearance of fringes in the M 2 C carbides coincided with the onset of overaging, i.e., aging at or above 510 ЊC. One reasonable explanation for these observations is that, until peak hardening, the ''M 2 C carbides'' are in the form of zones that are coherent with the matrix. The absence of fringes up to peak aging suggests that the precipitates may not have a crystalline structure of their own. It may, however, be argued that the absence of fringes may be due to the smaller size of the carbides and/or poor diffracted intensity rather than the lack of a crystal structure. Based on the present study, it is not possible to unambiguously claim that the fringe formation is the result of ''crystallization'' of the carbides. However, the present results along with the observation in the previous studies that diffraction patterns up to peak aging showed diffused intensity streaks along ͗100͘ ␣ are strongly suggestive that the carbides could be in the form of zones until overaging. [16,17] High resolution studies are underway to analyze the carbide structure in the peak hardened condition. REFERENCES 1.The Al-Si-Mg base cast alloys are widely used for structural applications. Mechanical properties and fracture behavior of these alloys depend on macrodefects such as internal oxide layers and shrinkage macroporosity, [1,2] microporosity, [3,4] dendrite cell size, [5,6] and size and shape of Si particles [7] present in the interdendritic regions. Fracture and debonding of silicon particles is an important aspect of damage evolution in these alloys. [3,[7][8][9] Fracturing/debonding of silicon particles, formation and growth of voids around such particles, and subsequent interlinkage of the voids lead to crack propagation in the interdendritic regions. Figure 1 illustrates this fracture micromechanism. It is observed that silicon particles fracture/debond at stresses significantly below the ultimate tensile strength, but usually above yield stress of the material. [7] There have been numerous studies on effect of tensile strain on the fraction of damaged* par-*''Damaged'' includes fractured and/or debonded silicon particles. ticles in Al-Si-Mg base alloys. [7,10] The damaged silicon particles are observed at very low plastic strain levels, and the fraction of damaged particles monotonically increases with the tensile strain. [7,10] However, in the earlier investigations, the mechanical tests were performed at room temperature only. To the best of the authors' knowledge, no experimental data on the effect of temperature on the microstructural damage exi...

Effects of vibration frequency on microstructure, mechanical properties, and fracture behavior of A356 aluminum alloy obtained by expendable pattern shell casting

“…It can be explained by the fact that the sample without vibration has the larger SDAS value and elongated eutectic silicon particles. The elongated eutectic silicon particles fracture more frequently than the spherical particles as they are the main sources of stress concentration [25][26][27]. Because the eutectic silicon particles are larger and cluster along both cell and grain boundaries, there is a nearly continuous wall of eutectic silicon particles around the dendrite cell.…”

Mechanical properties and fracture behavior of thixoformed, rheocast and gravity-cast A356 alloy

“…It has been reported that large and elongated silicon particles fracture more frequently than spherical particles [18][19][20][21]. In the case of thixoformed samples formed at 600 • C (Fig.…”

Numerical study of the casting features on the fracture and debonding of Mg17Al12 in AM60B Mg alloy under high cycle fatigue condition

“…Considerable effort has been made recently to investigate the effect of Si particles on the mechanical and fatigue properties of cast Al alloys, both experimentally and numerically [1][2][3][11][12][13][14][15][16]. However, the influence of the fracture and debonding of Mg 17 Al 12 particles on the fatigue characteristics of Mg alloys has not been well investigated until now.…”