Reduced-Pressure Foaming of Aluminum Alloys

Abstract

We developed a novel process for foaming aluminum and its alloys without using a blowing agent. The process involves a designated apparatus in which molten aluminum and its alloys are first foamed under reduced pressure and then solidified quickly. Foaming was done for pure aluminum (99.99 pct) and AlMg5 alloy not containing stabilizing particles and AlMg5 and AlSi9Mg5 alloys containing 5 vol pct SiO₂ particles. We discuss the foaming mechanism and develop a model for estimating the porosity that can be achieved in this process. The nucleation of pores in foams is also discussed.

Appendix

For calculating the reduced pressure P _RP , we consider that P _atm = 1 bar and define

$$ P'_{RP} = \frac{{P_{RP} }}{{P_{\text{atm}} }} $$

Rearranging Eq. [4] gives

$$ V_{2} \times \frac{1}{{M_{{}} }} \times \frac{1}{{S_{{{\text{H}}({\text{atm}})}} }} \times \frac{{T_{1} }}{{T_{2} }} = \left( {1 - \sqrt {P'_{RP} } } \right) \times \frac{1}{{P'_{RP} }} $$

(A1)

or

$$ \left( {V_{2} \times \frac{1}{{M_{{}} }} \times \frac{1}{{S_{{{\text{H}}({\text{atm}})}} }} \times \frac{{T_{1} }}{{T_{2} }}} \right) \times P'_{RP} + \sqrt {P'_{RP} } - 1 = 0 $$

(A2)

which is a quadratic equation of type $ax^{2} + bx + c = 0$ with coefficients

$$ a = \left( {V_{p} \times \frac{1}{{M_{{}} }} \times \frac{1}{{S_{{{\text{H}}({\text{atm}})}} }} \times \frac{{T_{1} }}{{T_{2} }}} \right),\,\,b = 1,\,\,c = - 1,\,\,{\text{and}}\,\,\,x = \sqrt {P'_{RP} } $$

and has the solution

$$ P'_{RP} = x^{2} = \left( {\frac{{ - b \pm \sqrt {b^{2} - 4ac} }}{2a}} \right)^{2} $$

(A3)

The P _RP calculated from Eq. [A3] has two solutions due to + ve and – ve signs in equation. Both solutions are given in Table I in columns 7 and 8.