Clearly Understand the Important Role of Aluminum in Superalloys

What is Aluminum

Aluminum is a silver-white light metal. Commodities are often made into bars, sheets, foils, powders, strips and wires. The content of aluminum in the earth's crust is second only to oxygen and silicon, ranking third, and it is the most abundant metal element in the earth's crust. The unique properties of aluminum and aluminum alloys have contributed to the development of the three important industries of aviation, construction, and automobiles.

	I																	O
1	1 H	II											III	IV	V	VI	VII	2 He
2	3 Li	4 Be											5 B	6 C	7 N	8 O	9 F	10 Ne
3	11 Na	12 Mg	III	IV	V	VI	VII	VIII			I	II	13 Al	14 Si	15 P	16 S	17 Cl	18 Ar
4	19 K	20 Ca	21 Sc	22 Ti	23 V	24 Cr	25 Mn	26 Fe	27 Co	28 Ni	29 Cu	30 Zn	31 Ga	32 Gc	33 As	34 Se	35 Br	36 Kr
5	37 Rb	38 Sr	39 Y	40 Zr	41 Nb	42 Mo	43 Tc	44 Ru	45 Rh	46 Pd	47 Ag	48 Cd	49 In	50 Sn	51 Sb	52 Te	53 I	54 Xe
6	55 Cs	56 Ba	57-71 La-Lu	72 Hf	73 Ta	74 W	75 Re	76 Os	77 Ir	78 Pt	79 Au	80 Hg	81 Tl	82 Pb	83 Bi	84 Po	85 At	86 Rn
7	87 Fr	88 Ra	89-103 Ac-Lr	104 Rf	105 Db	106 Sg	107 Bh	108 Hs	109 Mt	110 Ds	111 Rg	112 Uub

La-Lu		57 La	58 Ce	59 Pr	60 Nd	61 Pm	62 Sm	63 Eu	64 Gd	65 Tb	66 Dy	67 Ho	68 Er	69 Tm	70 Yb	71 Lu
Ac-Lr		89 Ac	90 Th	91 Pa	92 U	93 Np	94 Pu	95 Am	96 Cm	97 Bk	98 Cf	99 Es	100 Fm	101 Md	102 No	103 Lr

Item Name: Aluminum
Element Symbol: Al
Atomic Number: 13
Atomic Weight: 26.98
Atomic Radius: 143pm
Density: 2.7g/cm3
Melting Point: 660°C
Boiling Point: 2327°C
Electronic Layout: [Ne]2s23p1

Figure 1
The Atomic Structure of Aluminum

Physical Properties

The color of aluminum is silvery white. Aluminum is malleable. It has low density, good electrical and thermal conductivity, and high reflectivity.

Chemical Properties

Aluminum is an active metal. In dry air, a dense oxide film with a thickness of about 50 angstroms will be immediately formed on the surface of aluminum, so that the aluminum will not be further oxidized and can withstand water. However, when aluminum powder is mixed with air, it is extremely flammable. Molten aluminum can react violently with water. Aluminum is amphoteric, it is very soluble in strong alkalis and also soluble in dilute acids.

Solid Solution Strengthening Effect of Aluminum

The atomic radius of aluminum is larger than that of nickel, and it can play a solid solution strengthening effect in the superalloy matrix. However, only 20% of the aluminum in the superalloy enters the matrix, so the effect of solid solution strengthening is relatively limited.

The Precipitation Strengthening Effect of Aluminum

Aluminum plays a key role in precipitation strengthened superalloys (such as Inconel 718, Inconel X-750, Incoloy A-286, etc.). In the alloy, 80% of aluminum will form Ni3Al with nickel. This intermetallic compound will be precipitated from the γ austenite matrix to form a γ' phase, resulting in precipitation strengthening.

718

X-750

A-286

The higher the aluminum content in the alloy, the greater the number of γ' phases, and the more obvious the precipitation strengthening effect. The figure below shows the change in the content of the γ' phase and the yield strength of the alloy as the aluminum content increases.

Figure 2
The Change in the Content of the γ' Phase and the Yield Strength of the Alloy as the Aluminum Content Increases.

However, in precipitation strengthened superalloys, more aluminum is not the better. A proper amount of aluminum can increase the creep strength of the alloy, but when the content of aluminum exceeds a peak value, a large number of harmful phases will be precipitated in the alloy, and the creep strength of the alloy will drop drastically. Therefore, the content of aluminum is generally controlled below 2.8%. The figure below shows the relationship between alloy creep rupture time and aluminum content.

Figure 3
The Relationship between Alloy Creep Rupture Time and Aluminum Content

Conclusion

In superalloys, only a small part of aluminum plays a role of solid solution strengthening. A large amount of aluminum is involved in precipitation strengthening, which greatly improves the mechanical strength of the alloy.

The content of aluminum is generally controlled below 2.8%. Too much aluminum content will reduce the creep strength of the alloy.

AEETHER CO., LIMITED produce cost-effective Monel, Inconel, Incoloy & Hastelloy products. If you have any requirements, you can send inquiry to our E-mail:

[email protected]

✔ E-mail has been Copied

2021.12.13