PSI - Issue 7

C. Garb et al. / Procedia Structural Integrity 7 (2017) 497–504 C. Garb et Al. / Structural Integrity Procedia 00 (2017) 000–000

499

3

Table 1 Overview of alloy and component specifications Abbreviation Component Alloy

Modifier

Heat treatment

Specimen positions

ch AlSi8 Sr T5 cc AlSi8 Sr T6

cylinder head

AlSi8Cu3 AlSi8Cu3

Sr Sr

T5 T6

Pos 1.

crankcase Pos. 1-2 The dendrite arm space (DAS) for each alloy specification and specimen position is measured and also the Vickers Hardness at room temperature (RT) is determined, see Table 2. Quasi-static tensile tests are executed at room temperature (RT) (Table 1) and at an elevated temperature of 150 °C (Table 3). The quasi-static tensile tests at elevated temperature are conducted in a heat chamber.

Table 2 Results of the quasi-static tensile tests and microstructural analyses of the specifications at room temperature Specification Rp0.1 (MPa) Rp0.2 (MPa) UTS (MPa) Ag (%)

DAS (µm)

Vickers Hardness(HV)

A (%)

ch AlSi8 Sr T5 Pos. 1 cc AlSi8 Sr T6 Pos. 1 cc AlSi8 Sr T6 Pos. 2

24 31 72

105 121 111

167 257 189

198 277

287 326 208

2.3 1.5 0.2

2.3 1.6

- 0.2 The specimen positions differ in DAS with the smallest value of 24 µm for ch AlSi8 Sr T5 Pos. 1 followed by cc AlSi8 Sr T6 Pos. 1 with 31 µm. The highest ultimate tensile strength (UTS) at room temperature is shown for the cc AlSi8 Sr T6 Pos. 1 with 326 MPa. Comparing the results of the quasi-static tensile tests at room temperature with results at the elevated temperature of 150°C, the strain of ch AlSi8 Sr T5 Pos. 1 and cc AlSi8 Sr T6 Pos. 1 significantly rises in comparison to cc AlSi8 Sr T6 Pos. 2. On the contrary, the drop of the UTS is less distinctive for cc AlSi8 Sr T6 Pos. 2 with 10 %, which exhibits the lowest UTS at room temperature. The reduction of the UTS for ch AlSi8 Sr T5 Pos. 1 and cc AlSi8 Sr T6 Pos. 1 is approximately equal with 19 %.

Table 3 Results of quasi-static tensile tests at 150 °C Specification Rp0.1 (MPa)

Rp0.2 (MPa)

UTS (MPa)

Ag (%)

A (%)

ch AlSi8 Sr T5 Pos. 1 cc AlSi8 Sr T6 Pos. 1 cc AlSi8 Sr T6 Pos. 2

164 236 175

184 245

234 265 187

3.3 1.9 0.2

5.3 3.0 0.2

-

3. Fatigue tests The high-cycle fatigue tests are executed with cylindrical specimens at a load ratio of R=-1 under tension compression loading. The tests are conducted on a hydraulic testing machine at a testing frequency of 30 Hz. The experiments at the elevated temperature are performed utilizing a heat chamber. Every tested specimen exhibits the same pre-heating time period before test start to ensure equal testing conditions. The examined cylindrical samples possess a testing diameter of 6 mm, but differ in their length due to differences in the component design. The resulting S/N-curves are statistically determined by the standardized ASTM E739 (ASTM, 1998) procedure for the finite life regime and the arcsin √ p method introduced by Dengel (1975) for the run out region. The S/N-curves exhibit a second negative inverted slope k 2 in the run-out region which is five times the first negative inverted slope k 1 , this approach is also presented in McKelvey et al. (2012); Sonsino and Dieterich (1991). The number of load cycles for the run-outs is defined with 10 7 . The following S/N-curves show the resulting data points separated by the failure mechanism, which will be discussed later on in this work. In Fig. 1, the S/N-curves for ch AlSi8 Sr T5 Pos. 1 are presented for room and elevated temperature (150 °C). The number of cycles for the transition region N D between k 1 und k 2 rises to higher cycle numbers for the results with 150 °C testing temperature.