Microstructure, Mechanical Properties and Die-Filling Behavior of High-Performance Die-Cast Al-Mg-Si-Mn Alloy

doi:10.1007/s40195-015-0332-7

Abstract

Abstract:

This work aims to reveal the relationships between the microstructure, mechanical properties and flow behavior of die-casting AlMg₅Si₂Mn alloy. Results indicated that the microstructure of the die-cast AlMg₅Si₂Mn consists of α₁-Al grains, fine-size α₂-Al grains and (Al + Mg₂Si) eutectic. The surface layer observed has the thickness in a range of 120-135 μm, while an ellipse-like surface layer edge is observed in the corner of the plate-like sample. Tensile strength and elongation (δ) of the specimens are slightly decreased along the die-filling direction due to the backflow of melt. Pure (Al + Mg₂Si) eutectic layer and ultra-fine-size α₂-Al grains observed are around the overflow channels. Mass feeding is predominantly responsible for the superior mechanical properties of the round bars as compared to those of plate-like samples.

Key words: High-pressure die casting, Aluminum alloy, Microstructure segregations, Mechanical properties, Die-filling behavior, Numerical simulation

Zu-Qi Hu, Xin-Jian Zhang, Shu-Sen Wu. Microstructure, Mechanical Properties and Die-Filling Behavior of High-Performance Die-Cast Al-Mg-Si-Mn Alloy[J]. Acta Metallurgica Sinica (English Letters), 2015, 28(11): 1344-1353.

Figures/Tables 13

Fig. 1 a HPDC plates, b standard round tension test bar pointed by the arrow, c self-developed vacuum valve in the upside of the die

Table 1 Experimental die-casting parameters employed in current work

T _d	T _m	P	v ₁	v ₂
200 °C	700-710 °C	100 MPa	0.3 m/s	3 m/s

Fig. 2 Schematics of the tensile specimens (unit: mm): a locations of the A-type tensile specimens, b A-type specimen, c B-type specimen, d C-type specimen

Table 2 Chemical compositions of the different types of die-casting specimens (wt%)

Process	Specimen type	Mg	Si	Mn	Fe	Ti	Al
HPDC/HVDC	A	6.9	1.98	0.54	0.13	0.085	Bal
HPDC	B	5.7	1.94	0.57	0.16	0.09	Bal
HPDC	C	5.5	1.8	0.55	0.15	0.085	Bal

Table 3 Thermal physical parameters adopted in simulations

Parameter	Value
Latent heat of fusion	4.95 × 10⁹ J/g
Solidification range	813-898 K
Density	2.5 g/cm³
Thermal conductivity of liquid	1.88 × 10⁷ W/m K
Specific heat	1.153 × 10⁷ J/kg K

Fig. 3 Typical microstructures of the transverse cross section of HPDC AlMg5Si2Mn plate samples in different locations: a center part, b surface and subsurface, c dilatant shear band, d higher magnification of the dotted box in c

Fig. 4 Microstructures from the die-cast plates sectioned longitudinally: a inlet transverse of the castings showing the gate area (enclosed by the dotted box) and the die-filling direction heads into the page, b longitudinally cross-sectional area near the gate from the solid line in a, c higher magnification of the dotted box in b and the surface layer edge is enclosed by the dotted lines, d longitudinally cross-sectional area around the line 2 in a

Fig. 5 Microstructure from the die-cast plates sectioned transversely: a transverse of the castings showing the overflows area (enclosed by the dotted box) and the die-filling direction is out of the page, b corner of the cross-sectional area near the overflow from the line 1 in a, c middle part of the cross-sectional area near the overflow from the line 1, d higher magnification of the dotted box in c, e transversely cross-sectional area near the overflow from the line 2 in a and the regions pointed by the solid arrows represent the pure eutectic region

Fig. 6 Mechanical properties of the specimen section from different locations a and different specimen types b

Fig. 7 Simulation results of the contour of liquid alloy at different die-filling degrees: a 40%, b 50%, c 60%, d 65%, e 75%, f 80%

Fig. 8 Schematics of the formation of the ellipse-like surface layer edge: a melt flow during solidification, b microstructures in different locations

Fig. 9 Schematics of the formation mechanism of the microstructure around the overflows: a melt front advance to the overflow, b ESCs are blocked around the overflow, c liquid alloy preferentially solidified around the overflow, d die-filling process completed

Table 4 Comparison of the densities of B and C specimens

Process specimen	HPDC-B type	HVDC-B type	HPDC-C type
Density (g/cm³)	2.593	2.602	2.641

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