PSI - Issue 33

Maria Beatrice Abrami et al. / Procedia Structural Integrity 33 (2021) 878–886 / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 1. Coefficient of friction as function of the distance. The wear rate obtained by interrupting the test at 100 m and 500 m of sliding distance is reported in Fig. 2. For each case studied, wear rate is higher in the first 100 m because of the faster material removal in the initial stage of testing, before the steady condition is achieved. Greater standard deviations can also be noted, because of larger variations of the wear track width in the initial part of the test, during which the wear track has not been stabilized yet. Furthermore, a significant increase with temperature can be observed for wear rate measured at 100 m since adhesion and material removal are favored by the high temperatures. The negative effect of temperature on wear resistance of Scalmalloy® disappears for longer test, in fact, after 500 m, the wear rate is comparable for the sample tested at 25, 100 and 150 °C, only at 200°C a light increase of wear rate is noticeable. Moreover, the wear rate measured after 500 m at room temperature appears lower than that found in literature for AlSi10Mg alloy as built under similar test conditions (1.8 × 10 -3 mm 3 /Nm, Lorusso et al. 2016), disclosing a better wear resistance of AlMgScZr. This is due to AlMgScZr fine grain microstructure together with the Al 3 (Sc,Zr) precipitates that make this material harder and more isotropic than AlSi10Mg, which consists instead of α-Al phase and eutectic.

Fig. 2. Wear rate vs temperature for 100 and 500 m of distance.

1.2. Microhardness and microstructure Microhardness was evaluated after pin on disk tests in order to reveal possible microstructural variations. Results are reported in Fig. 3, where a great stability in microhardness values can be appreciated also after exposure soaking up to 200 °C for 7 hours. This fact suggests that no microstructural changes occurred with temperature for AlMgScZr alloy.