Blistering in semi-solid die casting of aluminium alloys and its avoidance

Hu, X. G.1,2,3; Zhu, Q.1,4; Midson, S. P.1,5; Atkinson, H. V.3; Dong, H. B.3; Zhang, F.1; Kang, Y. L.2

2017-02

10.1016/j.actamat.2016.11.032

ACTA MATERIALIA   影响因子和分区

1359-6454

1873-2453

Semi-solid die casting of relatively high solid-fraction aluminum alloys (0.5-0.7 fraction solid) can be used for the production of high quality industrial components. However, surface blistering during solution heat treatment can still be a problem and is associated with the entrapment of gas whether from air or from burned lubricant. Here the mechanism for formation of blisters is presented. The Reynolds number in the surface layer of the semi-solid flow is then analysed to obtain the relationships with hydraulic diameter and flow velocity for different slurry temperatures. The hypothesis is that it is some flow instability at the flow front, even where the overall nature of the flow is essentially laminar, which is leading to the entrapment. The crucial finding is that if the Reynolds number is plotted against temperature there is a decrease followed by an increase. The position of this minimum is dependent on the ratio of fill velocity to the hydraulic diameter, v/D. Thus there is a 'sweet spot' in terms of temperature (i.e. fraction liquid), flow velocity and hydraulic diameter (i.e. die design) where the flow front has the maximum stability, giving maximum resistance to blister formation. This is in contrast with conventional wisdom which would suggest that low fractions liquid would give the most stable flow front. A rationale for this is presented in terms of the particle crowding at the relatively low fraction of liquid. Experimental results with aluminium alloy 319s as an exemplar, and a die which has varying cross sectional dimensions, are presented and validate the hypothesis.

Blistering Semi-solid die casting Process window Heat treatment Aluminium alloy 319s

SCI ; EI

英语

通讯

National Key Research and Development Program of China[2016YFB0301001]

Materials Science ; Metallurgy & Metallurgical Engineering

Materials Science, Multidisciplinary ; Metallurgy & Metallurgical Engineering

WOS:000393000800045

PERGAMON-ELSEVIER SCIENCE LTD

20164803051979

Die casting ; Dies ; Flow velocity ; Heat treatment ; Liquids ; Reynolds number

Foundries:534.1 ; Foundry Practice:534.2 ; Heat Treatment Processes:537.1 ; Aluminum Alloys:541.2 ; Fluid Flow:631 ; Fluid Flow, General:631.1

MATERIALS SCIENCE

Web of Science

1.Gen Res Inst Nonferrous Met, Beijing 100088, Peoples R China
2.Univ Sci & Technol Beijing, Beijing 100083, Peoples R China
3.Univ Leicester, Dept Engn, Leicester LE1 7RH, Leics, England
4.Southern Univ Sci & Technol, Shenzhen 518055, Peoples R China
5.Colorado Sch Mines, Golden, CO 80401 USA

Hu, X. G.,Zhu, Q.,Midson, S. P.,et al. Blistering in semi-solid die casting of aluminium alloys and its avoidance[J]. ACTA MATERIALIA,2017,124:446-455.

Hu, X. G..,Zhu, Q..,Midson, S. P..,Atkinson, H. V..,Dong, H. B..,...&Kang, Y. L..(2017).Blistering in semi-solid die casting of aluminium alloys and its avoidance.ACTA MATERIALIA,124,446-455.

Hu, X. G.,et al."Blistering in semi-solid die casting of aluminium alloys and its avoidance".ACTA MATERIALIA 124(2017):446-455.