Effect of Phosphorus and Strontium Additions on Formation Temperature and Nucleation Density of Primary Silicon in Al-19
- PDF / 503,083 Bytes
- 6 Pages / 593.972 x 792 pts Page_size
- 63 Downloads / 151 Views
DUCTION
HYPEREUTECTIC Al-Si–based alloys continue to attract interest because of their good wear and corrosion resistance, low thermal expansivity, and low density.[1–3] Optimum mechanical properties require refinement of primary silicon as well as effective modification of the eutectic matrix. Attempts to achieve this by simultaneous additions have been frustrated, however, by destructive interactions between P-based refiner and Na- or Sr-based modifier.[4] The present work was carried out to investigate the effects of phosphorus and strontium additions on primary silicon formation from small melts of Al-19 wt pct Si alloy at different cooling rates. Our earlier article[5] reviewed the effect of cooling rate T_ and phosphorus inoculation on the number per v of primary silicon particles in hypereuunit volume N tectic Al-Si alloys. Most of the published results showed v ) with a good fit (within a factor of 3 in N v ¼ AT_ n N
½1
Here n = 1 and A = 130 mm3 (K/s)1 in the absence of phosphorus addition, and n = 1 and A = 720 mm3(K/s)1 in the presence of 0.1 to 0.2 wt pct P addition. Any attempt to model such size refinement of the primary silicon requires knowledge of the effect of M. FARAJI, formerly Ph.D. Student with the Department of Engineering Materials, University of Sheffield, is Lecturer in Metallurgy, Department of Materials, University of Semnan, Semnan 351311911, Iran. Contact e-mail: [email protected] I. TODD, Reader in Metallurgy, and H. JONES, Emeritus Professor of Metallurgy and Materials, are with the Department of Engineering Materials, University of Sheffield, Sheffield S1 3JD, United Kingdom. Manuscript submitted October 9, 2008. Article published online May 14, 2009 1710—VOLUME 40A, JULY 2009
variables on the temperature range over which the primary silicon forms. Terai[6] reported increased undercooling (i.e., decreased formation temperature, T1) to form primary silicon with increased cooling rate regardless of whether P or Na was added, with added P increasing T1 and added Na decreasing T1 at each cooling rate. Crosley and Mondolfo[7] also reported lower T1 when Na was added rather than P. Colligan and Gunes[8] reported formation of primary silicon at lower T1 from P-refined melts. Tenekedjiev et al.[9] reported decreased T1 on Sr addition with or without P addition to Al-17 wt pct Si alloy,* and Chang et al.[10] reported *The data in their Table III for Sr added alone, however, contradict this.
decreased T1 with increased rare earth addition to Al-21 wt pct Si alloy. Kyffin et al.[11] found a primary silicon arrest at some 50 K undercooling for Al-20 wt pct Si, which disappeared when 100 ppm P was present. Zhang et al.[12] reported formation of primary silicon at higher temperature when P was added to Al-25 wt pct Si. Song et al.[13] reported that 0.02 wt pct P raised the primary silicon start temperature T1 by 5.5 K in their BH135 alloy. Nogita et al.[14] reported that addition of 50 to 360 ppm Sr reduced the primary silicon reaction temperature of Al-17 wt pct Si by some 40 K, while Robles Hernandez
Data Loading...
