## 2 Experimental  
The material employed in the current work was commercial AlSi5 Cu1 Mg (Table 1) alloy and modified alloys containing 0.3, 0.6 and 0.9 wt % of La. The details of this process were as follows: four alloys with the basic composition of AlSi5 Cu1 Mg alloy at 1053 K were melted in a quartz crucible inside a furnace for 45 min. In addition, three of the melts were added with 0.3 wt %, 0.6 wt % and 0.9 wt % La (in the form of Al-10 wt % La master alloy).  
The microstructures of the alloys were observed by optical microscopy (Eclipse MA200, Nikon Metrology, Inc., Brighton, UK). The microstructural evolution, morphological changes in the compounds and effect of La addition were also investigated. Vickers hardness of casting samples was obtained by using the HV 1000 A hardness tester device (Laizhou Huayin Testing Instrument Co., Ltd., Laizhou, China). The sample was cut using a spark wire-cutting machine to make a small cylinder with a diameter and a height of 10 mm. The parallelism between the measured surface and the bottom surface is less than 0.01 mm. The measured surface of the sample was polished to a roughness less than 0.1 \(\upmu\)m. The samples were tested at room temperature. The sample was tested ten times on a selection of different region loading forces of 200 gf successively, and the loading positions (black prism) were shown in Figure 1a. It took 15 s to load the sample each time. Finally, a corresponding experimental report was generated.  
The tribological properties were determined in MMD-1 (Jinan Yihua Tribology Testing Technology Co., Ltd., Jinan, China) pin-on-disc apparatus at an ambient temperature of 25 \(\pm\) 3 \({}^{\circ}\)C. The wear tests were performed in a laboratory atmosphere with a relative humidity ranging from 40% to 60%. The wear tests were performed by the method known as unidirectional sliding pin on disc, where a pin  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Si** & **Mg** & **Cu** & **Zn** & **Fe** & **Mn** & **Al** \\ \hline
4.5–5.5 & 0.4–0.6 & 1.0–1.5 & \textless{}0.3 & 0.6–1.0 & \textless{}0.5 & Balance \\ \hline \hline \end{tabular}
\end{table}
Table 1: Main chemical composition of the AlSi5 Cu1 Mg alloy (wt %).  
was spun clockwise relative to the disc by the rotation radius of 18 mm, and all the tests were carried out without introducing any lubricant into the contact area. The wear test was shown in Figure 1b schematically. Castings were machined into 4.5 mm diameter and 11 mm length pins. C45E4 steel with a hardness of 55 HRC was used as the rotating disc. Prior to each test, the pin and disc surfaces were ground with 2000-grit SiC abrasive paper and cleaned in ethanol using an ultrasonic device. Wear tests were conducted with normal loads of 20, 60 and 100 N (respectively equivalent to 1.3, 3.8 and 6.3 MPa) meanwhile operating with sliding velocity of 100 and 300 r/min (equivalent to 0.19 and 0.57 m/s, respectively) for 10 min. The real-time friction coefficient can be generated directly from the MMD-1 device. The worn surface was studied by a scanning electron microscope (SEM, VEGA3, TESCAN CHINA, Ltd., Shanghai, China) with an energy dispersive spectrum (EDS). Before the scanning, the pins have been cleaned in ethanol using an ultrasonic device for 5 min. The weight loss of the samples was obtained by weighing the pin before and after each test using FA2204B electronic balance, and converted to volume loss by using the density of each sample.