Effect of Squeeze Casting on Microstructure and Mechanical Properties of Hypereutectic Al-xSi Alloys

doi:10.1016/j.jmst.2017.02.004

Abstract

Abstract:

The effect of squeeze casting on microstructure and mechanical properties of hypereutectic Al-xSi alloys (x = 15, 17.5, 22 wt%) was investigated in this study. Results show that microstructure of the hypereutectic Al-xSi alloys was obviously improved by squeeze casting. The amount of coarse primary Si phase decreased, while that of fine primary α-Al dendrites increased with the increase of squeeze casting pressure. Due to the decrease of coarse primary Si particles, cracking of the matrix was reduced, whilst the fine microstructure, and mechanical properties of the squeeze casting alloys were improved. Compared with gravity casting alloys, mechanical properties of the hypereutectic Al-xSi alloys solidified at 600 MPa were improved significantly. Hardness of the squeeze casting hypereutectic Al-(15, 17.5, 22 wt%) Si alloys was improved by 15.91%, 12.23%, 17.48%, ultimate tensile strength was improved by 37.85%, 32.27%, 22.74%, and elongation was improved by 55.83%, 167.86%, 126.76%, respectively. Due to the uniform distribution of Si phases in squeeze casting Al-xSi alloys, their wear resistance was markedly enhanced.

Key words: Hypereutectic Al-Si alloys, Squeeze casting, Microstructure, Mechanical properties, Primary Si phases

Li Runxia, Liu Lanji, Zhang Lijun, Sun Jihong, Shi Yuanji, Yu Baoyi. Effect of Squeeze Casting on Microstructure and Mechanical Properties of Hypereutectic Al-xSi Alloys[J]. J. Mater. Sci. Technol., 2017, 33(4): 404-410.

Figures/Tables 9

Fig. 1. Squeeze casting and gravity casting specimens (a) and the selected regions for OM analysis (b).

Fig. 2. Effect of pressure on microstructure of the investigated alloys: (a) Al-15 wt% Si alloys, gravity casting; (b) Al-15 wt% Si alloys, squeeze casting; (c) Al-17.5 wt% Si alloys, gravity casting; (d) Al-17.5 wt% Si alloys, squeeze casting; (e) Al-22 wt% Si alloys, gravity casting; and (f) Al-22 wt% Si alloys, squeeze casting.

Table 1 Metallographic parameters of primary Si particles of hypereutectic Al-xSi alloys (x = 15, 17.5 and 22 wt%) by gravity casting and squeeze casting.

Methods	Percentage of area (%)			Mean diameter (μm)			Count per unit area (10^-4/μm²)
	15Si	17.5Si	22Si	15Si	17.5Si	22Si	15Si	17.5Si	22Si
Gravity casting	4.77	7.30	9.21	17.61	25.88	27.15	1.22	1.28	1.82
Squeeze casting	0.26	0.39	0.72	5.59	9.22	14.30	0.08	0.14	0.49

Table 2 Comparison of primary Si sizes of hypereutectic Al-Si alloys prepared through different methods.

Methods	Alloys	Mean diameter of primary Si (μm)	Literature
Squeeze casting	Al-15Si	5.59	This work
	Al-17.5Si	9.22
	Al-22Si	14.30
Near-liquidus semi-continuous casting	A390	10.00	[6]
Ultrasonic vibration	A390	20.00	[10]
Nd modification	Al-17.5Si	10.00-30.00	[11]
Control diffusion solidification (CDS)	Al-18Si	42.85	[12]
Liquid-liquid mixing CDS	Al-15Si	14.00	[13]
Melt thermal treatment and modification on solidification	Al-20Si	10.00	[14]
Liquid-liquid mixing CDS	Al-20Si	37.00	[15]

Fig. 3. Schematic diagram of the effect of pressure on phase diagrams of Al-Si alloys: (a) 1.0 × 10-4 GPa, (b) 1.0 GPa, (c) 2.5 GPa, (d) 5.0 GPa, and (e) 600 MPa.

Fig. 4. Effect of squeeze casting on mechanical properties of Al-xSi alloys (x = 15, 17.5 and 22 wt%): (a) Brinell hardness; (b) ultimate tensile strength; and (c) elongation.

Fig. 5. Effect of squeeze casting on tensile fracture morphology of the alloys: (a) Al-15 wt% Si alloys, gravity casting; (b) Al-15 wt% Si alloys, squeeze casting; (c) Al-17.5 wt% Si alloys, gravity casting; (d) Al-17.5 wt% Si alloys, squeeze casting; (e) Al-22 wt% Si alloys, gravity casting; and (f) Al-22 wt% Si alloys, squeeze casting.

Fig. 6. Effect of squeeze casting on wear loss of Al-xSi alloys (x = 15, 17.5 and 22 wt%).

Fig. 7. Effect of squeeze casting on wear surfaces of Al-xSi alloys (x = 15, 17.5 and 22 wt%): (a) Al-15 wt% Si alloys, gravity casting; (b) Al-15 wt% Si alloys, squeeze casting; (c) Al-17.5 wt% Si alloys, gravity casting; (d) Al-17.5 wt% Si alloys, squeeze casting; (e) Al-22 wt% Si alloys, gravity casting; (f) Al-22 wt% Si alloys, squeeze casting.

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