I. Aluminum Alloys vs. Titanium Alloys: The "Division of Labor" in Aerospace Applications
|
Features |
Aluminum Alloy |
Titanium Alloy |
|---|---|---|
|
|
|
|
|
Strength |
|
|
|
Thermal intensity |
|
|
|
Corrosion resistance |
Good (must be aluminum-clad) |
Excellent (better than stainless steel) |
|
Machinability |
Good (easy to machine and weld) |
A little Difficult to process |
|
Costs |
Low (abundant aluminum resources) |
High (titanium ore is scarce and difficult to process) |
|
Aviation Applications |
Skin, main beams, fuel tanks (used extensively) |
Landing gear, engine components, high-temperature structures (critical areas) |
II. Titanium Alloys: "The Strength Backbone of High-End Structures"
Titanium is a "rare metal," but it has exceptional properties and is considered a "high-end material" in the aerospace industry.
1. Pure titanium: "Basic but difficult to machine" Key characteristics: Low density (4.5 g/cm³, 57% that of steel); high melting point (1660°C, 300°C higher than steel); non-magnetic (does not become magnetized in strong magnetic fields, making it suitable for avionics); extremely high corrosion resistance (stable in seawater, nitric acid, and dilute sulfuric acid, even surpassing stainless steel); Disadvantages: Low strength (pure titanium σb = 200–300 MPa); difficult to machine (poor thermal conductivity leads to tool wear during cutting; at high temperatures, it readily absorbs oxygen, nitrogen, and hydrogen, becoming hard and brittle).
2. Titanium Alloys: "Enhanced 'All-Rounders'" By adding alloying elements (aluminum, tin, vanadium, molybdenum, etc.), the drawbacks of pure titanium are addressed, resulting in high specific strength, high thermal strength, and high corrosion resistance.
3. Commonly Used Grades of Titanium Alloys in Aviation: GR5 (Ti-6Al-4V): The "classic titanium alloy" in aviation, accounting for over 80% of titanium alloy usage; Properties: High strength at moderate temperatures (below 400°C; σb = 1000 MPa) and good ductility (elongation of 10%); Applications: Compressor discs and blades (engines), landing gear support beams (Boeing 747), structural components (used as forgings in the annealed condition, and as fasteners after solution annealing); TC10 (Ti-6Al-4V + tin-copper-iron): Offers better heat resistance (operating below 450°C), used for engine compressor housings and high-temperature structural components;
III. Aluminum Alloys: From "Pure Aluminum" to "High-Strength Alloys"
Aluminum is the "foundational light metal" of the aerospace industry, but pure aluminum is too soft and must be strengthened by adding alloying elements (such as magnesium, manganese, copper, zinc, and silicon) to meet the structural requirements of aircraft.
1. Industrial-grade pure aluminum: A "soft but useful" base material. Key characteristics: Low density (2.7 g/cm³, only one-third that of steel); good electrical conductivity (62% of copper at room temperature, but twice the conductivity per unit mass, making it commonly used for electrical wires); extremely high ductility (35% elongation in the annealed state, allowing it to be cold-pressed into aluminum foil and rivets) ; good corrosion resistance (a dense Al₂O₃ oxide film forms on the surface, isolating it from air). Disadvantages: too low strength (σb = 78 MPa in the annealed state, equivalent to 1/10 that of steel), cannot be directly
The strength of aluminum alloys is enhanced through "solution treatment and aging" (heat treatment strengthening) and work hardening (cold deformation strengthening).
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