25 results about "Exfoliation corrosion" patented technology

The invention relates to a structure regulation and control method for reducing exfoliation corrosion sensitivity of an aluminum-lithium alloy and the aluminum-lithium alloy, and belongs to the field of alloy heat treatment. The method comprises the following steps: homogenizing an aluminum-lithium alloy ingot to obtain a homogenized alloy; and then the homogenized alloy is subjected to deformation treatment, solution treatment, step quenching and aging treatment in sequence, and the alloy is obtained. The deformation amount of the deformation treatment is 70-95%; the temperature of the solution treatment is 500-540 DEG C, and the time is 2-5 hours; the system of step quenching is a scheme (a) or a scheme (b). According to the scheme (a), the alloy is cooled to 400-450 DEG C and kept for 1-5 min, and then water quenching cooling is conducted to 10-30 DEG C; according to the scheme (b), the alloy is cooled to 250-300 DEG C and kept for 5-20 min, and then the alloy is cooled to 10-30 DEG C through water quenching. According to the method, the exfoliation corrosion sensitivity of the aluminum-lithium alloy can be effectively reduced by regulating and controlling the grain shape of the surface layer of the alloy and blocking a corrosion channel.

The utility model provides an aluminum alloy exfoliation corrosion test device, and relates to the technical field of aluminum alloy exfoliation corrosion tests. The handle is fixedly connected to the surface of the box body and used for assisting the box body in position movement; the liquid discharging pipe is fixedly connected to the surface of the box body and used for discharging liquid and aluminum alloy in the box body; the mounting pipe is slidably connected to the inner wall of the box body and is used for assisting in mounting the beaker; the placing hook is placed on the surface of the mounting pipe and is used for placing a beaker; and the limiting device is arranged in the box body and is used for further limiting the placed beaker. Through the arrangement of the limiting device, the beaker can be further limited after being placed on the placing hook, so that the beaker cannot move when the beaker moves in the box body and liquid is injected into the beaker, and the stripping effect of aluminum alloy can be well observed after an experiment is finished; and thus, a worker can conveniently record data.

The invention discloses a strengthening method and a preparation process of a high-strength corrosion-resistant aluminum alloy, and relates to the technical field of aluminum alloy materials.The strengthening method comprises the following steps that 1-3% pre-stretching treatment is conducted on a 7-series aluminum alloy profile obtained after solid solution quenching, and a dislocation network with the dislocation density larger than or equal to 10 < 14 > m <-2 > is introduced; by controlling specific chemical components of the 7-series aluminum alloy, a foundation is laid for high performance of the material, by means of a pre-stretching-aging synergistic process, residual stress is released through plastic deformation in pre-stretching, follow-up machining deformation and stress corrosion cracking risks are reduced, a dislocation network formed by pre-stretching provides a large number of uniform nucleation points for a strengthening phase, and the stress corrosion cracking risk is reduced. By combining two-stage aging and stretching regulation, uniform dispersed precipitation of a nanoscale eta'phase is promoted, generation of a thick eta phase is inhibited, meanwhile, the nucleation tendency of a strengthening phase at a grain boundary is reduced, a fine discontinuous grain boundary precipitated phase and a narrow lean solute region are formed, intergranular corrosion resistance and exfoliation corrosion resistance are remarkably improved, and balance of strength, toughness and corrosion resistance is achieved.

The invention provides a high-strength high-toughness corrosion-resistant Al-Mg alloy material and a preparation method, the alloy material comprises a core layer and an edge layer, the edge layer is a pure aluminum layer, and the core layer is a high-magnesium aluminum alloy ingot; and the aluminum alloy material is obtained after three-stage homogenization treatment and rolling. The alloy material has high strength and excellent corrosion resistance, the intergranular corrosion weight loss is smaller than or equal to 3 mg / cm < 2 >, and the exfoliation corrosion rating is PB.

According to the high-strength-toughness corrosion-resistant aluminum alloy for the multi-cavity automobile profile and the preparation method of the high-strength-toughness corrosion-resistant aluminum alloy, recrystallization and grain growth can be effectively inhibited by optimizing chemical components of the high-strength-toughness corrosion-resistant aluminum alloy, homogenization treatment and two-stage aging treatment are combined, high dispersion and uniform precipitation of a strengthening phase are promoted, and the corrosion resistance of the high-strength-toughness corrosion-resistant aluminum alloy is improved. The precipitation strengthening effect is maximized, so that the prepared alloy has high strength and high toughness; besides, an Al-3Ti-C intermediate alloy is added as an alterant and is combined with rare earth elements, so that the alloy structure is more uniform, lattice defects and introduction of impurity elements can be reduced, and then excellent corrosion resistance is obtained; and electromagnetic stirring, ultrasonic treatment, homogenization treatment and two-stage aging treatment are combined, so that a precipitated phase is further promoted to be moderately coarsened and tends to be stable, the potential difference between the grain boundary and the intracrystalline is remarkably reduced, the intergranular corrosion and exfoliation corrosion capacities of the aluminum alloy are remarkably improved, meanwhile, part of internal stress is released, and the dimensional stability is improved.

The utility model provides an auxiliary device for processing exfoliated corrosion samples, which relates to the technical field of auxiliary processing of exfoliated corrosion samples and comprises an auxiliary frame. The pressing screw rod is in threaded connection with the surface of the auxiliary frame and is used for limiting and pressing the aluminum alloy sample; the clamping strip is fixedly connected to the lower surface of the auxiliary frame and used for helping the auxiliary frame and the vice to be combined together; the rotating device is arranged on the surface of the auxiliary frame, and the aluminum alloy sample is helped to be subjected to angle rotation so as to be conveniently machined; the limiting device is arranged on the side wall of the auxiliary frame, and the sample can be conveniently and quickly placed in the middle by adjusting the distance between two limiting blocks. By arranging the rotating device, after one side of the sample is machined, the side edge of the sample can be quickly adjusted, the sample does not need to be taken from the interior of the auxiliary frame to be placed again, the adjusting speed is increased as much as possible, the replacement process is more convenient, and the working efficiency is further improved.

The invention belongs to the technical field of integrated die casting, and particularly relates to a heat-crack-resistant and corrosion-resistant heat-treatment-free die-casting aluminum alloy, a structural part and a preparation method. According to the heat-treatment-free die-casting aluminum alloy, on the basis of a Zr-Cr-Fe coordinated regulation and control system, by regulating and controlling the component range and proportion of the Zr-Cr-Fe coordinated regulation and control system, Cr and Fe preferentially form a Chinese-character-shaped Al-Si-Cr-Fe phase, and a harmful needle-shaped Fe-rich phase is replaced; and meanwhile, Zr forms Al3Zr dispersed particles to refine crystal grains, so that the heat cracking tendency is reduced synergistically. And by regulating and controlling the component ranges of Cr, Mn, Zr and Mg and the weight ratio of Zn to Mg, intergranular corrosion and exfoliation corrosion are effectively inhibited, an MgZn2 and Mg2Si composite passivation layer is generated on the surface of the casting, and the corrosion resistance is further improved. Through the synergistic effect of multi-element alloy elements, high mechanical property, low hot cracking tendency and high corrosion resistance can be achieved without heat treatment, and the die casting is suitable for being used as an integrated die casting with strict requirements for comprehensive performance.

The application relates to a preparation method of an Al-5.8Zn-2.2Mg-0.2Er-0.12Zr aluminum alloy plate, and belongs to the field of aluminum alloy plate preparation, in particular to a preparation method of an Al-5.8Zn-2.2Mg-0.2Er-0.12Zr aluminum alloy plate. The purpose of the application is to greatly improve the corrosion performance of the Al-Zn-Mg alloy while the Al-Zn-Mg alloy has high strength. The elements contained are weighed, smelted, refined, filtered, cast, homogenized annealed, milled, hot-rolled, solid-solved, stretched, aged, and sawed into products. According to the composition of the alloy, the homogenization annealing, solid-solution stretching and aging process systems are matched, and two kinds of normal-temperature tensile strength and exfoliation corrosion results are obtained. The user can select according to the use environment, and the application can meet the needs of important engineering fields such as ships, ocean engineering and rail transit.

The invention relates to a manufacturing method of a marine corrosion-resistant aluminum alloy plate, in particular to a manufacturing method of a marine corrosion-resistant aluminum alloy plate produced by an air cushion furnace. The invention aims to solve the problem that the surface quality, the exfoliation corrosion performance and the intergranular corrosion performance of the existing marine aluminum alloy plate are not qualified. The method comprises the following steps: 1, carrying out semi-continuous casting to obtain a cast ingot of the corrosion-resistant aluminum alloy plate for the air cushion furnace production ship; (2) milling the surface of the cast ingot; (3) soaking and heating; (4) hot rolling; (5) cold rolling; the marine corrosion-resistant aluminum alloy plate produced by the air cushion furnace is qualified in size, surface quality, plate shape, mechanical property, exfoliation corrosion property and intergranular corrosion property. The method is applied to the field of aluminum alloy plate manufacturing.

The aluminum profile comprises, by mass, 0.60%-0.7% of Si, 0.10%-0.15% of Fe, 0.8%-0.12% of Cu, 0.15%-0.25% of Mn, 0.55%-0.65% of Mg, 0.14%-0.2% of Cr, 0.15%-0.003% of Zn, 0.03%-0.06% of Ti, smaller than or equal to 0.01% of Pb, smaller than or equal to 0.15% of the total content of other impurity elements and the balance Al, the alkali metal content Na is smaller than or equal to 0.0004%, the alkali metal content Ca is smaller than or equal to 0.0002%, and the hydrogen content is 0.15 ml / 100 g. The corrosion resistance of the 6005A aluminum alloy material is improved by reasonably adjusting the proportion of chemical components and the casting technological process, the corrosion resistance can be easily achieved through existing domestic aluminum alloy smelting and casting equipment, and the exfoliation corrosion resistance of the finally obtained aluminum alloy profile is obviously improved through the aluminum alloy with optimized components.

The application belongs to the field of aluminum alloy materials, and provides an aluminum alloy with a tensile strength exceeding 780 MPa and N-grade exfoliation corrosion and a preparation method thereof.The aluminum alloy comprises the following chemical components by weight percentage: Zn 10.0-12.0%, Mg 2.5-3.5%, Zr 0.08-0.25%, Ti 0.03-0.10%, Fe ≤0.10%, Si ≤0.10%, other impurities ≤0.05% individually, a total amount ≤0.15%, and the balance being Al.The preparation method comprises the following steps: alloy component distribution, water-cooled mold casting to obtain an alloy round ingot with a required specification; two-stage homogenization process treatment and extrusion process forming; two-stage solid solution and T6 peak aging, so that the tensile strength exceeds 780 MPa and the exfoliation corrosion resistance grade is N grade; and the prepared plate can be widely applied to lightweight components in the fields of aerospace, transportation and weapons.

The invention provides a 7-series aluminum alloy and a preparation method and application thereof. The preparation method comprises the following steps: preparing raw materials according to the components of the 7-series aluminum alloy; the raw materials are sequentially smelted and cast to obtain an aluminum alloy cast ingot; the aluminum alloy ingot is sequentially subjected to first-stage homogenization treatment at the temperature of 360-420 DEG C and second-stage homogenization treatment at the temperature of 460-480 DEG C, and an aluminum alloy ingot blank is obtained; performing deformation treatment on the aluminum alloy ingot blank to obtain an aluminum processing material; and the aluminum processing material is sequentially subjected to solution treatment and aging treatment, and the 7-series aluminum alloy is obtained. The composition content of the aluminum alloy is adjusted to reduce generation of refractory compounds, meanwhile, dispersed Mn-containing phase particles are formed through specific homogenization treatment, and the microstructure of the material is further improved through solid solution and aging treatment, so that the high strength is kept, and meanwhile, the mechanical property of the material is improved. The stress corrosion sensitivity is greatly reduced; the exfoliation corrosion resistance is improved; and the hydrogen embrittlement corrosion behavior is improved.

This application belongs to the field of integrated die casting technology, and more specifically, relates to heat-treatable die-cast aluminum alloys, structural parts, and preparation methods that are resistant to hot cracking and corrosion. The heat-treatable die-cast aluminum alloy provided in this application is based on a Zr-Cr-Fe synergistic control system. By controlling its composition range and ratio, Cr preferentially forms a Chinese character-shaped Al-Si-Cr-Fe phase with Fe, replacing the harmful needle-like Fe-rich phase; simultaneously, Zr forms Al3Zr dispersed particles to refine the grains, synergistically reducing the tendency for hot cracking. By controlling the composition range of Cr, Mn, Zr, and Mg, and the Zn / Mg weight ratio, intergranular corrosion and exfoliation corrosion are effectively suppressed, and a MgZn2 and Mg2Si composite passivation layer is formed on the casting surface, further improving corrosion resistance. Through the synergistic effect of multiple alloying elements, high mechanical properties, low hot cracking tendency, and strong corrosion resistance can be achieved without heat treatment, making it suitable for integrated die castings with stringent comprehensive performance requirements.

The application provides an aluminum alloy wire for 600MPa strength grade aluminum alloy electric arc additive pieces and a preparation method thereof, and belongs to the technical field of aluminum alloy wires.The aluminum alloy wire is mainly composed of aluminum (Al), zinc (Zn), magnesium (Mg), copper (Cu), strontium (Sr), zirconium (Zr), titanium (Ti), scandium (Sc), erbium (Er), cerium (Ce) and lanthanum (La). The preparation of the alloy comprises the following steps in sequence: (1) melting and casting; (2) homogenization treatment; (3) hot extrusion; (4) spiral rolling; (5) surfacing process; and (6) subsequent heat treatment. The maximum strength of the alloy can reach 600MPa, the elongation after fracture is 5.4%, and the exfoliation corrosion grade is PC grade.

The invention discloses a forging method and a characteristic structure of an exfoliation-corrosion-resistant 7-series aluminum alloy. The method comprises the following steps: preheating an alloy ingot to 330-350 DEG C, and carrying out multidirectional forging to obtain a primary forge piece; and the primary forge piece is sequentially subjected to annealing treatment and multi-directional forging and is air-cooled to the room temperature, and the high-strength steel is obtained. By means of the method, the recrystallization degree of the alloy can be improved, and a nested structure with large recrystallization grains and a large number of small-angle grain boundary substructures or deformed structures distributed in an intermingled mode is obtained. Due to the fact that the corrosion resistance of the small-angle grain boundary is higher than that of the large-angle grain boundary, the small-angle grain boundary penetrates into metal along with corrosion in the exfoliation corrosion process, the large-angle grain boundary is corroded preferentially, a recrystallization part is hollowed out, and when corrosion enters a substructure and the small-angle grain boundary part, the corrosion rate is reduced, and the corrosion depth is controlled. On one hand, the nested structure ensures the excellent comprehensive performance of the forge piece, and on the other hand, the forge piece under various conditions and directions presents an approximate exfoliation corrosion grade which can generally reach the EA grade.

The application discloses a high-corrosion-resistance hot-rolled thick plate and a preparation method thereof. The hot-rolled thick plate comprises the following components in percentage by mass: Mg 0.75-1.0 wt.%, Si 1.35-1.75 wt.%, Fe <=0.3 wt.%, Cr 0.1-0.25 wt.%, Cu <=0.1 wt.%, Zn <=0.15 wt.%, Ti <=0.15 wt.%, and the balance of Al and inevitable total impurities. The application adjusts the composition cost of the aluminum alloy material, effectively improves the aluminum alloy chemical composition and the peeling corrosion resistance, makes the tensile strength >=310Mpa, the yield strength >=270Mpa, the elongation A50 >=10%, makes the peeling corrosion test grade N, and fully meets the use requirements of the railway bridge support, and greatly prolongs the service life of the railway bridge support.

The present application relates to a kind of organization regulation method for reducing exfoliation corrosion sensitivity of aluminum lithium alloy and aluminum lithium alloy, belong to alloy heat treatment field.The method includes: aluminum lithium alloy ingot is treated, obtains homogenization state alloy;Again homogenization state alloy is sequentially deformed, solution treatment, grading quenching and aging treatment, namely obtains;The deformation of deformation treatment is 70~95%;Solution treatment temperature is 500~540 DEG C, time is 2~5h;Grading quenching system is scheme (a) or scheme (b):Scheme (a):alloy is cooled to 400~450 DEG C and keeps 1~5min then water quenching is cooled to 10~30 DEG C;Scheme (b):alloy is cooled to 250~300 DEG C and keeps 5~20min then water quenching is cooled to 10~30 DEG C.The method can effectively reduce the exfoliation corrosion sensitivity of aluminum lithium alloy by regulating alloy surface layer grain shape and blocking corrosion channel.

The invention discloses a preparation process of a high-corrosion-resistance 6XXX aluminum alloy slab ingot in the technical field of aluminum alloy material production, and the high-corrosion-resistance 6XXX aluminum alloy slab ingot comprises the following components in percentage by mass: 0.75-0.85% of Si, less than or equal to 0.2% of Fe, less than or equal to 0.25% of Cu, 0.1-0.2% of Mn, 1.2-1.3% of Mg, less than or equal to 0.15% of Zn, 0.1-0.15% of Cr, 0.05-0.08% of Er, less than or equal to 0.15% of Ti, less than or equal to 0.05% of single other elements, less than or equal to 0.15% of other elements and the balance of Al; the alloy melt smelting and standing temperature is not higher than 750 DEG C, a launder is baked to 200-400 DEG C, during casting, the melt enters a vacuum and rotary blowing degassing and impurity removal box, a plate type filter box and a tubular filter box in sequence, multi-layer composite aluminum melt purification treatment is carried out, and after an obtained high-quality slab ingot is subjected to subsequent processing treatment, the alloy with the tensile strength larger than or equal to 290 MPa and the tensile strength larger than or equal to 290 MPa can be obtained. The exfoliation corrosion level is not lower than PA level, the intergranular corrosion depth is not higher than 100 [mu] m, and the hydrogen content is not higher than 0.1 ml / (100g. Al).

The application provides a high-strength and high-thermal-stability Al-Cu-Mg-Si alloy and a preparation method thereof, and belongs to the technical field of aluminum alloys.The chemical composition of the Al-Cu-Mg-Si alloy according to the application and the mass percentage are as follows: Si 0.5-0.9%, Fe <=0.5%, Cu 3.9-5.0%, Mn 0.4-1.2%, Mg 0.2-0.8%, Zr 0.15-0.2%, Cr 0.1-0.2%, Ni <=0.1%, Zn <=0.25%, Ti <=0.15%, the content of single impurity <=0.05%, the total content of impurities <=0.15%, and Al is the balance.The yield strength of the Al-Cu-Mg-Si alloy according to the application is >=475 MPa, the tensile strength is >=540 MPa, the elongation after fracture is >=12%, and after exposure at 200 DEG C for 100 h, the tensile strength is >=210 MPa, the yield strength is >=188 MPa, and the exfoliation corrosion grade is EB.The aluminum alloy according to the application has improved strength and thermal stability, and the corrosion resistance and toughness still maintain a high level.

The application discloses an aluminum-lithium alloy with high strength and high exfoliation corrosion resistance, a preparation process and application thereof, and belongs to the technical field of aluminum-lithium alloy materials.The aluminum-lithium alloy comprises the following components in percentage by mass: Cu 3.0%-4.2%, Li 0.6%-1.5%, Mn 0.1%-0.6%, Zr 0.05%-0.4%, and Zn and Ag, and the balance of Al and inevitable impurities, wherein the mass ratio of Zn / Ag is 2.0-6.0, and the Zn addition amount is 0.2%-1.2%; or the Ag is replaced by Mg, the mass ratio of Zn / Mg is 0.8-3.0, and the Zn addition amount is 0.4%-1.2%. The preparation process comprises the following steps: batching and smelting, two-stage homogenization treatment, hot rolling, controlled temperature annealing, cold rolling, solid solution quenching and stepwise aging temperature control treatment. The application breaks through the technical bottleneck that the strength and corrosion resistance of the aluminum-lithium alloy are difficult to be simultaneously improved by optimizing the Zn / Mg or Zn / Ag ratio and the stepwise aging process.

The invention discloses a low-density high-strength corrosion-resistant aluminum alloy and a preparation method and application thereof, and the low-density high-strength corrosion-resistant aluminum alloy comprises the following components in parts by weight: 6.5-8.5 parts of Mg, 2.8-4.8 parts of Zn and Cult. The alloy is prepared from the following components in parts by weight: 0.5 part of Mn, 0.15 to 0.40 part of Zr, 0.05 to 0.15 part of Ti and Filt. 0.15 part by weight, Silt; and 0.12 part by weight. According to the low-density high-strength corrosion-resistant aluminum alloy and the preparation method and application thereof, the comprehensive performance of the prepared aluminum alloy material is remarkably improved, and the density lt is achieved; the yield strength is larger than or equal to 520 MPa, the tensile strength is larger than or equal to 560 MPa, the elongation is larger than or equal to 8%, the exfoliation corrosion level is superior to the EA level, and meanwhile the uniformity and machining precision of the microstructure are improved.

The application discloses a copper-free ultra-high-strength aluminum alloy and a preparation method thereof, and belongs to the field of aluminum alloy design and processing. The alloy composition is as follows: Zn is 8.00%-12.00%, Mg is 2.00%-3.00%, Zr is 0.05%-0.15%, Cr is <0.15%, Ti is <0.10%, Cu is <0.15%, the total amount of impurity elements such as Fe and Si is <0.05%, and the balance is Al. The preparation and processing technology comprises the following steps: alloy batching and smelting, homogenization treatment, hot extrusion or hot rolling, solid solution treatment and aging treatment, so that the aluminum alloy has the following properties: tensile strength UTS >700MPa, elongation after fracture δ >8%, EA-grade anti-exfoliation corrosion, and excellent surface smoothness. The alloy has high zinc and magnesium, low copper, and by strictly controlling micro-alloying elements and impurity elements, the alloy has extremely high strength, almost no micron-sized second phase, and can maintain surface smoothness, good oxidation coloring effect and corrosion resistance. The application has the advantages of simple process, low cost, suitability for large-scale industrial production, and the ability to meet the demand for high-performance aluminum alloys in the fields of consumer electronics, transportation, aerospace and the like.

The application belongs to the technical field of bridge support spherical crown and discloses a preparation method of a high-wear-resistance and anti-stripping corrosion type aluminum alloy bridge support spherical crown lining plate, which comprises the following steps: (1) preparation of aluminum alloy raw materials; (2) alloy smelting and casting: after the components of the aluminum alloy are melted, a refining agent is added to remove the oxide slag in the aluminum alloy melt after refining treatment; then the aluminum alloy melt is cast to obtain an aluminum alloy ingot in a condensation crystallizer; (3) hot rolling deformation; (4) cutting, hot extrusion and die forming: the aluminum alloy round plate is formed into an aluminum alloy bridge support spherical crown lining plate blank through hot extrusion and die forming; (5) solid solution and aging heat treatment: after the blank is subjected to heat preservation solid solution heat treatment, it is rapidly water quenched, and after the aluminum alloy bridge spherical crown lining plate blank subjected to solid solution water quenching is subjected to aging heat treatment, a high-strength, high-hardness, high-wear-resistance and high-anti-stripping corrosion aluminum alloy bridge spherical crown support lining plate blank is obtained; and (6) machining. The aluminum alloy bridge support spherical crown lining plate has high anti-stripping corrosion performance.

The invention relates to the technical field of alloys, in particular to an aluminum alloy for a vehicle body framework of a new energy passenger vehicle and a preparation method of the aluminum alloy. According to the alloy, on an aluminum-magnesium-silicon substrate, multi-element microalloying is carried out, and specially-made zirconium-rare earth oxide and carbon nanoparticles are introduced for strengthening. The preparation method comprises the following steps: firstly synthesizing nanoparticles, then smelting, carrying out two-stage homogenization, carrying out hot extrusion forming, and finally carrying out solid solution quenching and welding seam area nanoparticle coating treatment on the profile. The components and the process are effectively coordinated, so that the material has high strength, high plasticity, excellent welding performance and exfoliation corrosion resistance at the same time, the problems of high-plasticity inversion and welding softening of a traditional automobile body framework aluminum alloy are successfully solved, and a high-performance material solution is provided for light weight of new energy automobiles.

The invention discloses a preparation method of an ultra-thick 5083 aluminum alloy plate, and belongs to the field of aluminum alloy processing. In order to solve the problems that when an ultra-thick 5083 plate is prepared through a traditional technology, layering and tearing are prone to occurring during cold rolling, and performance unbalance is caused due to the low total machining rate, the method comprises the steps of smelting casting, saw milling, heating, hot rolling, annealing and cold rolling coiling, annealing is conducted at the temperature of 250-300 DEG C for 6-12 h after hot rolling and before cold rolling, grain boundary Mg2Al3 phases are redissolved or spheroidized, and internal stress is eliminated. The final plate can meet the indexes of 285MPa < = Rm < = 385MPa, Rp0.2 > = 200MPa, A > = 10%, intergranular corrosion weight loss < = 15mg / cm and exfoliation corrosion PB and above.