## 1 Introduction  
The continuous casting direct rolling (CCDR) process comprises continuous casting and hot-strip rolling [1, 2, 3, 4]. The CCDR process significantly features deformations that can be accomplished on the same production line. As for energy efficiency and costs caused by the labor and process, the CCDR process is regarded as a promising high-efficiency production technology in industrial applications. Compared with the traditional casting and extrusion processes, the CCDR process contributes to high-strength quenched microstructure formations exhibiting excellent mechanical properties [4, 5]. The materials applied in the CCDR process are mainly copper and iron-based alloys [2, 6]. Now, only steel and copper alloys have CCDR products; the aluminum alloy has a low melting point, a narrow solidification temperature range, and insufficient material strength, so there is no CCDR product. It is worth noting that CCDR technology for Al alloys has gradually aroused attention in recent years, but current reports on Al-Si alloys are still rare [3, 5, 7, 8]. Therefore, the Al-Si alloy, considered as highly fluid and with excellent wear resistance, was introduced to the CCDR process for the purpose of developing high wear-resistant materials used in the industry [3, 9, 10]. In previous literature, Si efficiently increased the fluidity of the Al alloy as a liquid state, inhibited its thermal expansion rate, and formed a Si solid solution in the Al matrix to improve the wear resistance [11; 12; 13; 14; 15]. The aforementioned properties contribute to this alloy wildly employed as a welding material for Al alloy parts and as a cylinder head or a lifter between the piston in engine systems [16]. According to the advantages reported in previous studies, combining the CCDR process with a potential Al-Si alloy can further improve the mechanical properties and considerably save production costs [3; 5]. Considering the cold workability of wire rods used in the production of a Al-Si alloy for high wear-resistant purposes, the rolling process was added after the CCDR process to compare the mechanical properties and wear resistance [17]. Nevertheless, cold rolling will also be accompanied by the disadvantage of a reduced ductility. The cold-worked wire bars would increase the ductility after the two-stage heat treatment for industrial applications [18; 19; 20]. In addition, reducing the residual stress and improving the ductility after cold working through recrystallization was contributed by the two-stage heat treatment, including a solid solution treatment and aging treatment [21]. The specimens after cold rolling were subjected to the solid solution treatment at 540 \({}^{\circ}\)C for 4 h (water quench) and aging at 170 \({}^{\circ}\)C for 12 h (air cooling) [22; 23]. The solid solubility of Si in Al is rare under 523 K in the Al-Si phase diagram, and Si precipitation would redissolve into the Al matrix after the solid solution treatment beyond this temperature [24]. Several studies have reported that the ceramic particles hit the metal specimens' surface at a high speed during particle erosion, and kinetic energy is transformed into heat, which can raise the temperature of the surface to 400-500 \({}^{\circ}\)C instantaneously [25; 26; 27]. This phenomenon of high temperature and local high stress effects the results in the phase transform (phase dissolved or formation) on the surface and has been demonstrated on other metal materials [26; 28; 29; 30]. The phase transform plays an important role, affecting the hardness and mechanical properties [29; 31; 32]. Therefore, the investigation of the phase transform mechanism and examination reliability after particle erosion in the CCDR Al-Si alloy subjected to different conditions is the main concept in this study. Compared with traditional processes, where the Al alloys are first cast, demolded, and cut into billets and then subjected to hot extrusion or rolling to form bars or plates of specific sizes, the CCDR process effectively reduces the production costs [2; 3].